message: Fix NPE relating to toggling notifications
  The fallthrough for `notifier_enabled` caused a NPE on `payload.error`, so this moves the fallthrough to where it is intended and sanity checks `payload.error` for next time.
diff: @@ -537,12 +537,12 @@ module.exports = React.createClass({
  case 'picture_snapshot':
  this.uploadFile(payload.file);
  break;
  - case 'notifier_enabled':
  case 'upload_failed':
  // 413: File was too big or upset the server in some way.
  - if(payload.error.http_status === 413) {
  + if (payload.error && payload.error.http_status === 413) {
  this._fetchMediaConfig(true);
  }
  + case 'notifier_enabled':
  case 'upload_started':
  case 'upload_finished':
  this.forceUpdate();
  