better error flows on failure to reattach

[slingamn]

@bogdomania was connecting to an always-on client using The Lounge. Since the browser-to-TL connection was plaintext, TL correctly did not send the secure flag with its WEBIRC command. This meant that the new client connection did not have modes.TLS, forbidding reattach:

https://github.com/oragono/oragono/blob/a83dc6e10dadf2815ca2ee5fbe8d30b31916957a/irc/client_lookup_set.go#L208

Since this cannot be corrected by sending a new NICK line, the error should be fatal in this case. In general, these cases should have better error messages even when a non-fatal 433 ERR_NICKNAMEINUSE is correct.

[DanielOaks]

Just curious, could you mention why the new NICK line wouldn't be able to fix this? Is it because useAccountName was in use or something different in the flow that's non-obvious? (mostly curious where I missed the error flow as well aha)

[DanielOaks]

Oh I see, always-on was in use which forces nick == account name. yeah that makes more sense then, bring on the fatal errors!

[slingamn]

That's a good point --- the error should only be fatal if nick-equals-account is enabled (either via the explicit nick-equals-account setting, or because it's an always-on account).