glx: Fix a corner case in DrawableGone

Losing the drawable does not change our notion of current client.  Since
the GL under us doesn't understand having a current context without
current drawables (sigh), we do still need to loseCurrent so that we
re-bind the context on the next request.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=65030
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Signed-off-by: Adam Jackson <ajax@redhat.com>

glx/glxext.c

@@ -139,8 +139,8 @@ DrawableGone(__GLXdrawable * glxPriv, XID xid)
         next = c->next;
         if (c->currentClient &&
 		(c->drawPriv == glxPriv || c->readPriv == glxPriv)) {
+            /* just force a re-bind the next time through */
             (*c->loseCurrent) (c);
-            c->currentClient = NULL;
             if (c == __glXLastContext)
                 __glXFlushContextCache();
         }