Blender Git Loki

Fix T74425: Cannot texture paint an images sequence anymore

Caused by the introduction of UDIM (rBc30d6571bb47).

We need to make sure the tiles ImageUser is set up correctly [especially
the framenr], otherwise BKE_image_acquire_ibuf() and friends will fail
to find the correct ImBuf.

Also instead of initializing a minimal BKE_imageuser_default, now use
an appropriate ImageUser if avaliable and pass this around (instead of
just the tile_number). 2D painting can reuse the Image Editor ImageUser,
for 3D painting we still rely on a default ImageUser in most places, but
at least set the framenr correctly].

This also fixes crashes when doing image operations such as inverting or
resizing on images in a sequence in the Image Editor.

This also fixes color sampling (S) from the 3DView going wrong for image
sequences (would fallback to OpenGL sampling because an ImBuf could not
be found).

Maniphest Tasks: T74425

Differential Revision: https://developer.blender.org/D7022