Fix Registration Bug

Summary

After submitting the email in the registration and clicking on signup one is not lead to the final signup screen which tells the user that everything went well and which redirects him/her to the start screen. Instead the email screen keeps being visible and one can click on signup again, which in turn leads to an error (that's ok, because the registration confirmation email was already sent at this point).

Steps to reproduce

Create a new user: when at email input page, provide the email, click "signup".

What is the current bug behavior?

No navigation to next screen.

What is the expected correct behavior?

Navigate to final signup screen. Signup button shouldn't be visible anymore if everything went well.

Relevant logs and/or screenshots

See completion_screen.dart and signup_screen.dart

Possible fixes

Problem lies probably somewhere here:

signup_screen.dart:146

case 2:
 registrationNotifier
 .checkEmailValid(emailFieldController.text);
 if (registrationState.isEmailValid) {
 await registrationNotifier.register(
  SignupFormular(
   usernameFieldController.text,
   passwordEvaluationFieldController.text,
   emailFieldController.text,
   1));
  if (registrationState.isSuccess) {
   controller.nextPage(
    duration: const Duration(milliseconds: 300),
    curve: Curves.ease);
  }
 }
 break;