Video Player: Add null-check on playback error

BUG=none
TEST=none
TBR=fukino@chromium.org

Review URL: https://codereview.chromium.org/507173004

Cr-Commit-Position: refs/heads/master@{#292078}

ui/file_manager/video_player/js/video_player.js

@@ -105,7 +105,7 @@ FullWindowVideoControls.prototype.showErrorMessage = function(message) {
  * @private
  */
 FullWindowVideoControls.prototype.onPlaybackError_ = function(error) {
-  if (error.target &&
+  if (error.target && error.target.error &&
       error.target.error.code === MediaError.MEDIA_ERR_SRC_NOT_SUPPORTED) {
     this.showErrorMessage('GALLERY_VIDEO_ERROR');
     this.decodeErrorOccured = false;