SanitizePublicHTTPURL rejected a hostname as soon as any single resolved
address was blocked, so a resolver returning a bogon AAAA for the test URL
host (e.g. 2001::1 for www.google.com, inside the Teredo range blocked
since b51f0976) failed the outbound Check button outright — including TCP
mode, which never uses the test URL. Mirror SSRFGuardedDialContext instead:
one usable address is enough, because the guarded dialer skips blocked
answers at connect time; a hostname with nothing usable is still refused.
Closes#6290
Sanaei