Survey navigation is not working when triggering completeness check twice

[ywarnecke]

The navigation logic is currently faulty, when reaching the completeness check a second time.

Steps to reproduce:

1. Create Bundle with multiple questionnaires with mandatory questions
2. Start survey; Skip mandatory questions
3. Upon completeness validation, navigate back, leave question unanswered
4. Second completeness check will throw an error and show an empty white screen

[ywarnecke]

Closed in #276