The rest of blender does handle multi-layer EXR images, using the
"combined" or RGBA/RGB layers when the visual result is needed. Make
VSE do the same.
While fixing this, I found several issues in other not well tested code
and had to fix them:
- IMB_buffer_float_from_float_threaded was wrongly using source channels
as destination channels, producing garbage result.
- IMB_scale_into_new was not assigning channels to destination image.
Pull Request: https://projects.blender.org/blender/blender/pulls/132790
5ef08c2a96