message: fix: page might be null'ed before clearHistory's navigatedToEvent
diff: @@ -374,10 +374,9 @@ export class PageRouterOutlet implements OnDestroy { // tslint:disable-line:dire
  if (this.outlet) {
  this.routeReuseStrategy.clearCache(this.outlet.outletKeys[0]);
  }
  - page.off(Page.navigatedToEvent, clearCallback);
  });
  - page.on(Page.navigatedToEvent, clearCallback);
  + page.once(Page.navigatedToEvent, clearCallback);
  }
  this.frame.navigate({
  