Blender Git Loki

Fix crash when adding strip using RNA API call

Don't allocate StripElem for movieclip, scene and mask strips. This
struct is not handled in seq_dupli function. This caused field to be
uninitialized in COW datablock.

StripElem is not allocated when adding strip with operator and it is
not needed for these strip types.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D9600