dbus: Fix a crash in UpdateEngineClientImpl::OnGetStatusError()

|error| can be NULL if the response is not received.

BUG=316986
TEST=none

Review URL: https://codereview.chromium.org/68533009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234474 0039d316-1c4b-4281-b951-d872f2087c98
Mojo: More plumbing to support sending handles over MessagePipes.

R=darin

Review URL: https://codereview.chromium.org/68993005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234475 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234474
SVN changes up to revision 234475