Bug 1802685 - Prevent error when searching on server in nntp-js. r=mkmelin

Differential Revision: https://phabricator.services.mozilla.com/D163393

--HG--
extra : amend_source : 232181df7eed26e30fab696c837eaaae52002e0b

mailnews/news/src/NntpClient.jsm

@@ -831,7 +831,7 @@ class NntpClient {
    * @param {NntpResponse} res - XPAT response received from the server.
    */
   _actionXPatResponse({ status, statusText, data }) {
-    if (status != XPAT_OK) {
+    if (status && status != XPAT_OK) {
       this._actionError(NNTP_ERROR_MESSAGE, statusText);
       return;
     }