Bug 378468 - remove warnings from nsDocAccessible::InvalidateCacheSubtree, r=ginn.chen

accessible/src/base/nsDocAccessible.cpp

@@ -1408,9 +1408,6 @@ NS_IMETHODIMP nsDocAccessible::InvalidateCacheSubtree(nsIContent *aChild,
     // event for it
     GetAccService()->GetAccessibleFor(childNode, getter_AddRefs(childAccessible));
   }
-  nsCOMPtr<nsPIAccessible> privateChildAccessible =
-    do_QueryInterface(childAccessible);
-  NS_ENSURE_STATE(privateChildAccessible);
 
 #ifdef DEBUG_A11Y
   nsAutoString localName;
@@ -1431,8 +1428,11 @@ NS_IMETHODIMP nsDocAccessible::InvalidateCacheSubtree(nsIContent *aChild,
       aChangeEventType == nsIAccessibleEvent::EVENT_REORDER) {
     // Fire EVENT_HIDE if previous accessible existed for node being hidden.
     // Fire this before the accessible goes away.
-    privateChildAccessible->FireToolkitEvent(nsIAccessibleEvent::EVENT_HIDE,
-                                             childAccessible, nsnull);
+    nsCOMPtr<nsPIAccessible> privateChildAccessible =
+      do_QueryInterface(childAccessible);
+    if (privateChildAccessible)
+      privateChildAccessible->FireToolkitEvent(nsIAccessibleEvent::EVENT_HIDE,
+                                               childAccessible, nsnull);
   }
 
   // Shutdown nsIAccessNode's or nsIAccessibles for any DOM nodes in this subtree