
As in the commit mentioned below, we dropped the only place where
current_gl_draw_buffer is set. Which was still being used for glx and
ended up causing black screen with multi-monitors & nvidia.
Fixes: aa0600bf2
("cogl: Remove Framebuffer:stereo-mode")
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4323>