In blender 2.79 you could use a render result as a camera background
image. This is useful during layout/compositing. During Blender 2.80
development there were 2 changes that removed this feature.
- to receive a render result the image required a lock. This lock wasn't passed and therefore no image was read from the result. Generating an GPUTexture from an Blender image also didn't do the locking.
- the iuser->scene field wasn't set what is required for render results.
This change adds an optional ibuf parameter to GPU_texture_from_blender that can be passed when available.