During a SwapBuffers request, we may end up querying an unknown drawable
outside of an active context, and so need to report this error prior to
attempting to dereference the NULL context.
Also fixes:
[Bug 29184] glXSwapBuffers with no GLX context crashes X.
https://bugs.freedesktop.org/show_bug.cgi?id=29184
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Keith Packard <keithp@keithp.com>
7e58178060