mod_invites_register: Fix missing 'from' attribute (thanks Martin) This should probably cause a noisier error in Prosody, than the current > No hosts[from_host] (please report): <stanza> A stack trace would have been useful, for example.

This module writes out a traceback to `traceback.txt` in Prosodys data
directory (see `prosodyctl about`) when the signal `SIGUSR1` is
received. This is useful when debugging seemingly frozen instances in
case it is stuck in Lua code.