AllocAndFetchScreenConfigs always calls UnlockDisplay twice without an
intervening LockDisplay. We found this because XCB asserts that you can't unlock
the display if you don't have it locked.

While fixing this we noticed that SyncHandle isn't consistently called after
UnlockDisplay in this function.

--- glxext.c    26 Sep 2006 23:56:20 -0000      1.25
+++ glxext.c    6 Oct 2006 00:17:39 -0000
@@ -1016,11 +1016,11 @@ static Bool AllocAndFetchScreenConfigs(D
        if (!_XReply(dpy, (xReply*) &reply, 0, False)) {
            /* Something is busted. Punt. */
            UnlockDisplay(dpy);
+           SyncHandle();
            FreeScreenConfigs(priv);
            return GL_FALSE;
        }
 
-       UnlockDisplay(dpy);
        if (!reply.numVisuals) {
            /* This screen does not support GL rendering */
            UnlockDisplay(dpy);