[WK2] setMinimumLayoutWidth should bail if there's no WebProcess
https://bugs.webkit.org/show_bug.cgi?id=109512
<rdar://problem/13093627>

Reviewed by Anders Carlsson.

* UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::setMinimumLayoutWidth):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142542 268f45cc-cd09-0410-ab3c-d52691b4dbfc