oper vhosts are not validated

[slingamn]

You can set an oper vhost with a space in it, which is protocol-breaking:

@time=2021-06-29T12:36:29.013Z;msgid=ykih9r6gcqtv6qaipdiqcrrvr6 :asdf!~u@for all intents and purposes PRIVMSG #xyz :hi

I think this came up previously? Anyway, this should probably just be validated against vhosts.valid-regex even when user-set vhosts are disabled.

[slingamn]

This needs to be changelogged as a compatibility break, since it means that configurations that were previously considered valid will now fail to start.