Blender Git Loki

Fix T77994: VSE crash adding a glow effect strip

Since rB47f98a38d0f8 not all 3 effect inputs were assigned anymore. Their
ImBuf's rect was accessed though in do_glow_effect (even though unused in
the following dedicated functions).

Just pass NULL here instead.

Reviewed By: ISS

Differential Revision: https://developer.blender.org/D8064