mod_storage_appendmap: Fix keyvalue writes store_raw() takes a filename, unlike most other datamanager functions that take a series of path components, leading to this bug where it would write the hostname into a file named after the first argument (commonly a username) in the working directory.

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.