[opengl] Another possible fix for the BadMatch error

[Leon Freitag]

> The BadMatch in X_GLXCreateGLXPixmap is another problem.. here you
> should get a BadMatch in X_GLXMakeCurrent.

That's true, this patch should only fix the BadMatches in glXMakeCurrent.
> BadMatch in X_GLXCreateGLXPixmap is a known problem, I've submitted a
> patch but it was rejected.

Well, try to resubmit it :) Or post it here, so that others could test it. 
Perhaps you could merge this one-liner into it and then resubmit it.

Leon