mod_storage_xmlarchive: Fix "user" iteration API Fixes use in prosody-migrator. Otherwise this particular API is not used much, or this would have been noticed before. Usually it is a different store like 'accounts' that is responsible for providing the authoritative list of users. Thanks Ge0rG for testing

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.