Avoid error when creating forks and restricted levels are defined

What does this MR do?

This fixes a crash when forking a project when no restricted access levels are defined in the application settings.

The crash wash introduced in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16050

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/42607