Windows uses GL_BGRA, but e.g. on Linux OpenGL stores as GL_RGBA.

Change-Id: I00820f7b7a16a54b10c682ba332627ec04648508
Reviewed-on: https://gerrit.libreoffice.org/70772
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>