MUC: Ensure allow MUC PM setting has valid value (fixes #1933) In case allow PM is set to "affiliated" or something other than a valid role name, but the user is not affiliated, the valid_roles lookup would return nil, triggering a comparison error. This ensures that the setting is validated going in and out of the database and that the "affiliated" case proceeds correctly. Also adds a compat mapping for the value "anyone", used in XEP-0045 and submitted by default by Gajim.