If the destination texture is not FBO attachable GLSL blitter does not work
for it unless backbuffer is used as offscreen rendering mode.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=47121Signed-off-by: Paul Gofman <gofmanp@gmail.com>
Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>