Freeze break request: Fix crash for legacy fullscreen windows on map

["Jasper St. Pierre" <jstpierre mecheye net>]

When mutter thinks a window is fullscreen through the legacy code path
(it has the same size as the monitor, for example), it crashes. This
was introduced in a fix for focus stacking, which was added at the
last minute:

    https://bugzilla.gnome.org/show_bug.cgi?id=620744

Downstream bug report showing crash:

   https://bugzilla.redhat.com/show_bug.cgi?id=806437

Patch:

   http://fpaste.org/0Tfk/

I have confirmed locally that the patch fixes the issue.

-- 
  Jasper