Was caused by recent change in image_buffer_rect_update which
was writing data to ibuf-rect_float. Apparently, this buffer
could point to different render layer than came from RenderResult.
Made quick fix for this, which ends up in skipping float buffer
update in image_buffer_rect_update and skipping GLSL when image
has both byte and float buffers.
This will bring speed down a bit, but slower blender is better
than broken blender.
Proper fix will arrive later this week.
bfeef2f5f0