box: Check before using the LayoutManager instance
box: Check before using the LayoutManager instance

A ClutterBox might not have a ClutterLayoutManager instance
associated -- for instance, during destruction. We should check
for one before calling methods on it.

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