Prevent crash on login of no guest session

src/Notifier.js

@@ -1,5 +1,6 @@
 /*
 Copyright 2015, 2016 OpenMarket Ltd
+Copyright 2017 Vector Creations Ltd
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -14,8 +15,6 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-'use strict';
-
 var MatrixClientPeg = require("./MatrixClientPeg");
 var PlatformPeg = require("./PlatformPeg");
 var TextForEvent = require('./TextForEvent');
@@ -103,7 +102,7 @@ var Notifier = {
     },
 
     stop: function() {
-        if (MatrixClientPeg.get()) {
+        if (MatrixClientPeg.get() && this.boundOnRoomTimeline) {
             MatrixClientPeg.get().removeListener('Room.timeline', this.boundOnRoomTimeline);
             MatrixClientPeg.get().removeListener("Room.receipt", this.boundOnRoomReceipt);
             MatrixClientPeg.get().removeListener('sync', this.boundOnSyncStateChange);