mod_muc_badge: If room has no title use localpart of room's jid (fixes #1767) Without this patch Prosody shows an HTTP 500 error (Lua 5.1) or a "nil" label in the SVG badge (Lua 5.2) if room has no title set.

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.