gnome-desktop freeze break request

[Alexander Larsson <alexl redhat com>]

This is a very safe fix that fixes a gnome-settings-daemon crash:

https://bugzilla.gnome.org/show_bug.cgi?id=646714

Basically it just adds a NULL check, and if we hit the NULL check we
would have crashed previously but don't now.

I hit this while going fullscreen in a new resolution with the spice
client. (see https://bugzilla.redhat.com/show_bug.cgi?id=693296)

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 Alexander Larsson                                            Red Hat, Inc 
       alexl redhat com            alexander larsson gmail com 
He's an uncontrollable one-eyed inventor She's a wealthy insomniac journalist 
from out of town. They fight crime!