It's true that the value would always be -1, if it's not zero, but it's
usually zero is the problem. As a result we return failure from
otherwise successful indirect GLX paths, which isn't very nice of us.
This reverts commit 7d33ab0f8c.
Fixes: https://gitlab.freedesktop.org/xorg/xserver/issues/211
(cherry picked from commit e1fa3beb2f)