Ensure that the Image maintains the proper file path after saving all
the individual tiles.
The image_save_post function is unaware that the filepath it receives
is only for a single tile, not the entire Image, and happily keeps
setting ima->filepath to the concrete filepath for each tile.
There were 2 problems with the code that attempted to correct the
Image filepath back to the UDIM virtual form:
- It would trample the "relative" directory that might have been set
- It would do the wrong thing if no tiles could be saved at all
The design is now as follows: Example of trying to save to a new PathB
| | all tiles ok | any tile not ok|
| -------------------------------- | ---------------- | ---------------|
| ima->filepath is currently empty | set to new PathB | keep empty |
| ima->filepath is currently PathA | set to new PathB | keep PathA |
Differential Revision: https://developer.blender.org/D15384
f256201876