Breakage fix for patch for bug 637367 (4da037fe27b0). a=breakage-fix

layout/generic/nsObjectFrame.cpp

@@ -1985,7 +1985,8 @@ static void DrawPlugin(ImageContainer* aContainer, void* aPluginInstanceOwner)
 
 static void OnDestroyImage(void* aPluginInstanceOwner)
 {
-  NS_RELEASE(static_cast<nsPluginInstanceOwner*>(aPluginInstanceOwner));
+  nsPluginInstanceOwner* owner = static_cast<nsPluginInstanceOwner*>(aPluginInstanceOwner);
+  NS_IF_RELEASE(owner);
 }
 
 void