Blender Git Loki

Fix T93368: Dragging Blends Without Previews

Unfortunately the drop logic for file-path based drag & drop checks the
used icon for its logic. This is very bad and should be changed. But
doing this involves some changes that are better not done during bcon4,
so for now stick to it and update the icon check.

Reviewed by: Julian Eisel

Differential Revision: https://developer.blender.org/D13383?id=45314