fix crash on shutdown after reading news message in memory cache r=sspitzer, sr=mscott 65724

mailnews/news/src/nsNNTPProtocol.cpp

@@ -862,6 +862,9 @@ NS_IMETHODIMP nsNNTPProtocol::AsyncRead(nsIStreamListener *listener, nsISupports
         MarkCurrentMsgRead();
         if (NS_SUCCEEDED(rv)) // ONLY if we succeeded in actually starting the read should we return
         {
+          // we're not calling nsMsgProtocol::AsyncRead(), which calls nsNNTPProtocol::LoadUrl, so we need to take care of some stuff it does.
+          m_ContentType = "";
+          m_channelListener = nsnull;
           return rv;
         }
       }
@@ -5418,7 +5421,6 @@ nsresult nsNNTPProtocol::CleanupAfterRunningUrl()
       mailnewsurl->SetMemCacheEntry(nsnull);
   }
 
-
   PR_FREEIF(m_path);
   PR_FREEIF(m_responseText);
   PR_FREEIF(m_dataBuf);