When adding an IPv6 server by its IP, the server does not appear in the server list after relaunching the game.

This was initially reported unofficially nearly a year ago.

The cause of the bug appears to be that the `:` character is used to separate server name, address and port in `external_servers.txt`. A typical IPv4 server looks like this:
2:dev:192.168.0.9:19132:1515091629

whereas an IPv6 server looks like this:
15:laptop_ipv6:fe80::f4c8:1278:cbdc:f35a:19132:1515522225

The obvious problem being that the IPv6 address is then parsed incorrectly due to the colons.