Fix undefined method issue in test

[dwightwatson]

Motivation / Background

This Pull Request has been created because my test suite started failing at commit ref 27140247c21c3925ee971ca4437e9a7f6fe198a3, which comes from PR #50597.

Error:
UsersHelperTest#test_familiar_names_returns_ordered_familiar_names:
NoMethodError: undefined method `route_defined?' for nil
    test/helpers/users_helper_test.rb:7:in `block in <class:UsersHelperTest>'

Detail

I think the change in the above commit requires an additional safe navigation to route_defined? in order to preserve the same functionality from before the previous change and to fix the bug.

Additional information

Happy to provide a sample app demonstrating the bug if required.

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behaviour change or additional feature. Minor bug fixes and documentation changes should not be included.

[Edouard-chin]

You are right that it misses a safe navigation to behave as before. Can you please add a regression test in the Rails test suite ?