SASL race condition

There is a race condition in `server_auth_sasl` which causes a server running ShadowIRCd and its derivatives to segfault if the `AUTHENTICATE {base 64 data}` for the PLAIN mechanism is sent before the server replies with `AUTHENTICATE +` to indicate mechanism readiness. The offending code is not present in, for example, Charybdis, and commenting out this function call will disable every part of it without side effects. The commit related to this can be found here:

https://github.com/PonyChat/elemental-ircd/commit/f5ed1007bad4218e035a29bd572d9ff7acced6a8

Obviously, this