This removes ImageTile->ok and ImageUser->ok.
They had three possible values which (probably) had the following meanings:
- 0: There was an error while loading the image. Don't try to load again.
- 1: Default value. It will try to load the image.
- 2: The image was loaded successfully.
This image-wide flag did not make sense unfortunately, because loading may work for some frames of an image sequence but not for others.
My current understand is that the ->ok flags only existed as an optimization to avoid checking the file system over and over again when a file is missing.
To get this optimization back, the patch is changing MovieCache so that it can also cache failed load attempts. As a consequence, ibuf is allowed to be NULL in a few more places. I added the appropriate null checks.
This would be useful to avoid a hacky solution in D12827.