Video Player: fix misc bugs

ui/file_manager/video_player/js/video_player.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 'use strict';
 
 /**
  * @param {Element} playerContainer Main container.
  * @param {Element} videoContainer Container for the video element.
  * @param {Element} controlsContainer Container for video controls.
@@ skipping 576 matching lines @@
     }
   }
 };
 
 /**
  * Called when the current cast is disappear from the cast list.
  * @private
  */
 VideoPlayer.prototype.onCurrentCastDisappear_ = function() {
   this.currentCast_ = null;
-  this.currentSession_.removeUpdateListener(this.onCastSessionUpdateBound_);
-  this.currentSession_ = null;
+  if (this.currentSession_) {
+    this.currentSession_.removeUpdateListener(this.onCastSessionUpdateBound_);
+    this.currentSession_ = null;
+  }
   this.controls.showErrorMessage('GALLERY_VIDEO_DECODING_ERROR');
   this.unloadVideo();
 };
 
 /**
  * This method should be called when the session is updated.
  * @param {boolean} alive Whether the session is alive or not.
  * @private
  */
 VideoPlayer.prototype.onCastSessionUpdate_ = function(alive) {
@@ skipping 38 matching lines @@
 var initPromise = Promise.all(
     [new Promise(initVideos.wrap(null)),
      new Promise(initStrings.wrap(null)),
      new Promise(util.addPageLoadHandler.wrap(null))]);
 
 initPromise.then(function(results) {
   var videos = results[0];
   player.prepare(videos);
   return new Promise(player.playFirstVideo.wrap(player));
 }.wrap(null));