Fix region handling of broken mirrors

The handling of region vs broken mirrors (in state "f") is wrong,
and we might end up with the wrong URLs in foreign regions, like:

| # ./generate_mirror_map| sort -u
| at mirror.alwyzon.net/grml/|at.mirror.anexia.com/grml/
| br grml.c3sl.ufpr.br//
| ch mirror.de.leaseweb.net/grml/|ftp.halifax.rwth-aachen.de/grml/|mirror.23m.com/grml/
| cn mirror.de.leaseweb.net/grml/|ftp.halifax.rwth-aachen.de/grml/|mirror.23m.com/grml/
| de mirror.de.leaseweb.net/grml/|ftp.halifax.rwth-aachen.de/grml/|mirror.23m.com/grml/
| fi mirror.de.leaseweb.net/grml/|ftp.halifax.rwth-aachen.de/grml/|mirror.23m.com/grml/
| gb mirror.bytemark.co.uk/grml/
| hk mirror-hk.koddos.net/grml/
| ir mirror.bardia.tech/grml/
| nl mirror.koddos.net/grml/|mirror.nl.leaseweb.net/grml/
| tw tw1.mirror.blendbyte.net/grml/
| ua grml.ip-connect.info//|grml.ip-connect.vn.ua//
| us mirror.us.leaseweb.net/grml/|mirrors.rit.edu/grml/

Now with the fixed behavior, we get what we're expecting:

| # ./generate_mirror_map| sort -u
| at mirror.alwyzon.net/grml/|at.mirror.anexia.com/grml/
| br grml.c3sl.ufpr.br//
| de mirror.23m.com/grml/|mirror.de.leaseweb.net/grml/|ftp.halifax.rwth-aachen.de/grml/
| gb mirror.bytemark.co.uk/grml/
| hk mirror-hk.koddos.net/grml/
| ir mirror.bardia.tech/grml/
| nl mirror.nl.leaseweb.net/grml/|mirror.koddos.net/grml/
| tw tw1.mirror.blendbyte.net/grml/
| ua grml.ip-connect.info//|grml.ip-connect.vn.ua//
| us mirror.us.leaseweb.net/grml/|mirrors.rit.edu/grml/