culling: Use vertex_count not '4' to determine partial culls
culling: Use vertex_count not '4' to determine partial culls

We were mistakenly using the constant 4 to determine the number of
vertices that need to be culled for a paint-volume to be considered
fully culled too. This is only ok for 2d volumes and was resulting in
some 3d volumes being considered culled whenever 4 out of 8 vertices
were culled. This fix is simply to reference the vertex_count variable
instead of assuming 4.

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