Blender Git Loki

Fix T41411: Undo crashing with background images set.

Since 3DViews use IDs like images or clips, we can't skip anymore `lib_link_screen()`
when reading from mem for undo/redo stuff. Else, freeing (unused) screen in `BKE_read_file_from_memfile()`
will lead to using data already freed (since pointers have not been updated when reading that undo step).