Three cases beside the existing ingest ones, since the read route has the
same trap and one property of its own.
- the route exists and carries `auth_request`;
- it has no login fallback — with the browser location as the positive
control, so a pass means the two routes differ rather than that
`error_page` and the login host are absent from the whole vhost;
- it injects no filter, on `extraConfig` and on `proxyPass` both, because
VictoriaLogs takes its filters as request parameters and those ride an
upstream URI as easily as a directive. A filter arriving later is then a
visible diff here rather than a quiet change of rule.
Each absence arm leads with a clause that proves the location resolved and
that `hasInfix` finds what is really in that string, so "not there" cannot
be read off an unreadable path.
Refs #3870
fde4a36b93