message: Prevent crash on login of no guest session
  The bound functions are only set when the Notifier is started, so
  if stop() was called without start() having been called, the
  listener function would be null which would throw an exception.
diff: /*
  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);
  