thunderbird, npob, don't prompt/send mdn response when reading news messages, r/sr=sspitzer 209516

mail/base/content/mailWindowOverlay.js

@@ -2025,6 +2025,9 @@ function HandleMDNResponse(aUrl)
   if (!msgFolder || !msgURI)
     return;
 
+	if (IsNewsMessage(msgURI))
+		return;
+
   var msgHdr = messenger.messageServiceFromURI(msgURI).messageURIToMsgHdr(msgURI);
   var mimeHdr = aUrl.mimeHeaders;