close socket only if it exists

lib/nntp.js

@@ -178,7 +178,10 @@ NNTP.prototype.connect = function(options) {
         // many? servers don't support the *mandatory* CAPABILITIES command :-(
         if (err && cmd !== 'CAPABILITIES') {
           self.emit('error', err);
-          return self._socket.end();
+          if (self._socket) {
+            self._socket.end()
+          }
+          return;
         }
         // TODO: try sending CAPABILITIES first thing
         if (!cmd) {