* Fix wrong getHeader refactoring
Fix regression introduced by
https://github.com/FreshRSS/FreshRSS/pull/2373
The refactoring required a call to init() even for static functions,
which is most of the time not done.
Removed premature abstraction of `$_SERVER`, which was the root cause of
the bug.
https://github.com/FreshRSS/FreshRSS/issues/2748#issuecomment-569898931
* Refactoring: Move serverIsPublic to Minz_Request
* Add mitigations for wrong configurations
Due to the regression, we have some existing configurations with a bad
base_url
* Forgot one instance