Blender Git Loki

Fix T81594: Unable to reassign effect inputs

This was caused by canceling operator if strip has more than 0 inputs.
Logic should be reversed - cancel only if strip has 0 inputs.

BKE_sequencer_render_loop_check() arguments had to be sanitized because
seq_effect_find_selected() can set seq1,2,3 to NULL

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D9197