bug 851674: content: nsContentUtils::CheckForSubFrameDrop: don't dereference null pointer (r=smaug)

content/base/src/nsContentUtils.cpp

@@ -5293,7 +5293,7 @@ bool
 nsContentUtils::CheckForSubFrameDrop(nsIDragSession* aDragSession, nsDragEvent* aDropEvent)
 {
   nsCOMPtr<nsIContent> target = do_QueryInterface(aDropEvent->originalTarget);
-  if (!target && !target->OwnerDoc()) {
+  if (!target) {
     return true;
   }