glx: Do not access stage_clip without checking it
glx: Do not access stage_clip without checking it

The stage_clip parameter for add_redraw_clip() can be NULL, so we need
to check before accessing its members.

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