Fix undefined index in ManiphestTaskSummaryView

Summary:
Currently, my homepage raises a couple of these:

  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message: [2013-03-13 06:44:38] ERROR 8: Undefined index:  at [/INSECURE/devtools/phabricator/src/applications/maniphest/view/ManiphestTaskSummaryView.php:133]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #0 ManiphestTaskSummaryView::render() called at [/INSECURE/devtools/phabricator/src/applications/maniphest/view/ManiphestTaskListView.php:45]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #1 ManiphestTaskListView::render() called at [/INSECURE/devtools/phabricator/src/view/AphrontView.php:63]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #2 AphrontView::producePhutilSafeHTML() called at [/INSECURE/devtools/libphutil/src/markup/render.php:65]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #3 phutil_escape_html(Object ManiphestTaskListView)"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #4 array_map(phutil_escape_html, Array { 0 => Object ManiphestTaskListView }) called at [/INSECURE/devtools/libphutil/src/markup/render.php:120]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #5 phutil_implode_html(, Array { 0 => Object ManiphestTaskListView }) called at [/INSECURE/devtools/phabricator/src/view/layout/AphrontPanelView.php:92]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #6 AphrontPanelView::render() called at [/INSECURE/devtools/phabricator/src/view/AphrontView.php:63]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #7 AphrontView::producePhutilSafeHTML() called at [/INSECURE/devtools/libphutil/src/markup/render.php:65]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #8 phutil_escape_html(Object AphrontPanelView)"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #9 array_map(phutil_escape_html, Array of size 8 starting with: { 0 => Object AphrontPanelView }) called at [/INSECURE/devtools/libphutil/src/markup/render.php:85]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #10 phutil_escape_html(Array of size 8 starting with: { 0 => Object AphrontPanelView })"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #11 array_map(phutil_escape_html, Array of size 2 starting with: { 0 => Array of size 8 starting with: { 0 => Object AphrontPanelView } }) called at [/INSECURE/devtools/libphutil/src/markup/render.php:85]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #12 phutil_escape_html(Array of size 2 starting with: { 0 => Array of size 8 starting with: { 0 => Object AphrontPanelView } })"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #13 array_map(phutil_escape_html, Array of size 2 starting with: { 0 => null }) called at [/INSECURE/devtools/libphutil/src/markup/render.php:85]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #14 phutil_escape_html(Array of size 2 starting with: { 0 => null }) called at [/INSECURE/devtools/libphutil/src/markup/render.php:53]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #15 phutil_tag(div, Array of size 2 starting with: { class => phabricator-nav-content }, Array of size 2 starting with: { 0 => null }) called at [/INSECURE/devtools/phabricator/src/view/layout/AphrontSideNavFilterView.php:297]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #16 AphrontSideNavFilterView::renderFlexNav() called at [/INSECURE/devtools/phabricator/src/view/layout/AphrontSideNavFilterView.php:184]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #17 AphrontSideNavFilterView::render() called at [/INSECURE/devtools/phabricator/src/view/AphrontView.php:63]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #18 AphrontView::producePhutilSafeHTML() called at [/INSECURE/devtools/libphutil/src/markup/render.php:65]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #19 phutil_escape_html(Object AphrontSideNavFilterView)"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #20 array_map(phutil_escape_html, Array { 0 => Object AphrontSideNavFilterView }) called at [/INSECURE/devtools/libphutil/src/markup/render.php:120]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #21 phutil_implode_html(, Array { 0 => Object AphrontSideNavFilterView }) called at [/INSECURE/devtools/phabricator/src/view/page/PhabricatorBarePageView.php:58]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #22 PhabricatorBarePageView::willRenderPage() called at [/INSECURE/devtools/phabricator/src/view/page/PhabricatorStandardPageView.php:104]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #23 PhabricatorStandardPageView::willRenderPage() called at [/INSECURE/devtools/phabricator/src/view/page/AphrontPageView.php:46]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #24 AphrontPageView::render() called at [/INSECURE/devtools/phabricator/src/applications/directory/controller/PhabricatorDirectoryController.php:15]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #25 PhabricatorDirectoryController::buildStandardPageResponse(Object AphrontSideNavFilterView, Array { title => Phabricator }) called at [/INSECURE/devtools/phabricator/src/applications/directory/controller/PhabricatorDirectoryMainController.php:66]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #26 PhabricatorDirectoryMainController::buildMainResponse(Object AphrontSideNavFilterView, Array of size 8 starting with: { 5 => Object PhabricatorProject }) called at [/INSECURE/devtools/phabricator/src/applications/directory/controller/PhabricatorDirectoryMainController.php:27]"
  [13-Mar-2013 06:44:38] WARNING: [pool www] child 27678 said into stderr: "NOTICE: PHP message:   #27 PhabricatorDirectoryMainController::processRequest() called at [/INSECURE/devtools/phabricator/webroot/index.php:91]"

There two cases here:

  - There's no owner. In this case, we might-or-might-not have loaded the handle for the "empty" PHID, but we shouldn't try to render in either case.
  - There is an owner. In this case, we definitely should have loaded the handle, so it's fine for us to fatal if we didn't (it indicates a serious problem with the program).

Test Plan: Loaded home page, no errors.

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D5329