x11: Ignore NULL settings
x11: Ignore NULL settings

Prevent a segfault when dealing with XSETTINGS_ACTION_DELETE.

http://bugzilla.clutter-project.org/show_bug.cgi?id=2441

djdeath/clutter-multithreaded,nobled/clutter,jigpu/clutter,jigpu/clutter,djdeath/clutter-android,GNOME/clutter,Distrotech/clutter,Distrotech/clutter,nobled/clutter,Distrotech/clutter,jigpu/clutter,dlespiau/clutter,nobled/clutter,heysion/clutter-clone,collects/clutter,ebassi/clutter,djdeath/clutter-android,GNOME/clutter,djdeath/clutter,djdeath/clutter-android,Distrotech/clutter,kerrickstaley/clutter-vala,jigpu/clutter,djdeath/clutter-android,GNOME/clutter,kerrickstaley/clutter-vala,djdeath/clutter-multithreaded,heysion/clutter-clone,ebassi/clutter,collects/clutter,spatulasnout/clutter,jigpu/clutter,GNOME/clutter,heysion/clutter-clone,kerrickstaley/clutter-vala,spatulasnout/clutter,spatulasnout/clutter,djdeath/clutter,spatulasnout/clutter,heysion/clutter-clone,collects/clutter,dlespiau/clutter,djdeath/clutter-android,spatulasnout/clutter,ebassi/clutter,kerrickstaley/clutter-vala,djdeath/clutter-multithreaded,jigpu/clutter,djdeath/clutter,djdeath/clutter-multithreaded,collects/clutter,collects/clutter,GNOME/clutter,djdeath/clutter,Distrotech/clutter,ebassi/clutter,djdeath/clutter,dlespiau/clutter,djdeath/clutter,heysion/clutter-clone,ebassi/clutter,Distrotech/clutter