BLF_buffer was trying to accept "how many colors channels in output
image?" argument and doing math with it, but in the lowest level code
was always writing out full 4 channels for each pixel.
All the call sites would ever call it with argument of 4 however, and
that is why no one noticed the issue.
Pull Request: https://projects.blender.org/blender/blender/pulls/121630
008483fe8a