We were incorrectly NULLing out pDraw in __GLXDrawable instead of ours in
__GLXAquaDrawable. (we should refactor to eliminate this redundancy later)
This was causing http://xquartz.macosforge.org/trac/ticket/426
This was benign until commit f0006aa58f
The root cause of this change was fed7ccc481ad1caaa518cafe944c2327a5d0b6c65
Signed-off-by: Jeremy Huddleston <jeremyhu@apple.com>