Caused by rB2bf4c74130ff.
For undo, the ImageUser's scene should be NULL (see D7022 for
discussion).
PaintTiles were already doing it beforehand in ED_image_paint_tile_push,
but Image ops [scale/invert] are calling
ED_image_undo_push_begin_with_image directly.
Now actually set the UndoImageHandle iuser.scene to NULL (rather than
asserting)
ref T75675
Maniphest Tasks: T75675
Differential Revision: https://developer.blender.org/D7435
f250b1f5a0