randr: Don't send output property events on server exit

If the Window resource type is already gone, there's no point in trying
to send events, all it can do is access already-freed memory.

Relevant thread:

http://lists.freedesktop.org/archives/xorg/2008-November/040443.html

randr/rrproperty.c

@@ -59,7 +59,8 @@ DeliverPropertyEvent(WindowPtr pWin, void *value)
 
 static void RRDeliverPropertyEvent(ScreenPtr pScreen, xEvent *event)
 {
-    WalkTree(pScreen, DeliverPropertyEvent, event);
+    if (!(dispatchException & (DE_RESET | DE_TERMINATE)))
+	WalkTree(pScreen, DeliverPropertyEvent, event);
 }
 
 _X_EXPORT void