mod_http_muc_log: Fix exception on lack of trailing slash in room path A request to /room leads to the match call returning nil which in turn calls nodeprep(nil). In Prosody 0.11.x this does nothing and simply returns the nil, while in 0.12 it is an error. Now it redirects to the calendar view at /room/ - even for non-existant rooms. Discovered at a deployment with http_paths = { muc_log = "/" } and requests to /robots.txt and similar, which now result in a uses redirect before returning 404.

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.