Fix #28780: Undo while painting image sequences issue

Fix #28780: Undo while painting image sequences issue

- Store imbuf file path in UndoImageTile structure, so imbuf can be verified
  before applying titles on it.
- If current image's imbuf file path isn't equal to file path stored in
  undo block, search for imbuf in ima->ibufs.

  Probably it can be optimized, but storing all settings which defines
  needed imbuf (image source type, offset, image file name, current
  scene frame and so messes up undo code and requires deeper changes
  which probably better not to start on bcon4).