mod_sasl2_fast: Fix malformed-request when using HT-*-NONE (thanks lnj!) This crept into the previous commit which tried to fail early when CB was requested but unavailable - that commit did not actually check that CB *was* requested.

This module discards typing notifications sent to a bare host JID,
preventing error replies to be sent. These errors are harmless but can
be annoying sometimes if your client shows them prominently.