Caused by either rB465a9f65de76: Cleanup: remove window manager argument for paint cursor API or rB78017916f7c7: Fix error removing the image paint cursor.
Not sure if the above just exposed a bug/design flaw or if we are now
acting on the wrong cursor.
While there are probably better ways to do this [by letting
WM_paint_cursor_end() be a bit more selective/polling on what it kills],
we can also just do a "cleanup" pass after [using
ED_space_image_paint_update() to make sure the Image Editor is in the
right state].