actor: Use an explicit check for NULL
actor: Use an explicit check for NULL

Follow the coding style, and don't use the implicit C boolean
equivalence for NULL pointers.

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