Bug 587494: Check whether our ExternalResource has a viewer before calling Hide() on it, to fix null-crash. r=roc a=blocking

content/base/src/nsDocument.cpp

@@ -826,7 +826,9 @@ ExternalResourceHider(nsIURI* aKey,
                       nsExternalResourceMap::ExternalResource* aData,
                       void* aClosure)
 {
+  if (aData->mViewer) {
     aData->mViewer->Hide();
+  }
   return PL_DHASH_NEXT;
 }