Fixes typo in args passed to `get_term_link()` which caused a fatal error due to this call returning a `WP_Error` which was set to `url`. Also fixes never-satisfiable condition for obtaining post type archive URL. Also ensures that `WP_Error` never leaks through as `url` by setting it to an empty string. Adds missing unit tests.
Amends [38991].
See #38114.
Fixes#38945.
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