Purged users displayed as authors of public workflows

[jdavcs]

Describe the bug

Purged users displayed as authors of public workflows.

Galaxy Version and/or server at which you observed the bug
Galaxy Version: 24.1.4, main

Expected behavior
Do not display the username hash. Instead, display "anonymous user" (or something like that) + do not link to list of workflows published by that user.

Suggested follow-up
Consider whether there may be other cases where we might be displaying purged users.

Reported by @bgruening