Workaround for older bug in Xamarin.Forms by waiting for app to resume before attempting to set Application.Current.MainPage (#757)

src/App/Pages/Accounts/TwoFactorPageViewModel.cs

@@ -141,6 +141,7 @@ namespace Bit.App.Pages
                     page.DuoWebView.RegisterAction(sig =>
                     {
                         Token = sig;
+                        App.WaitForResume();
                         Device.BeginInvokeOnMainThread(async () => await SubmitAsync());
                     });
                     break;