fix(system_chat_message): Fixes delivering system messages to visitors.

resources/prosody-plugins/mod_fmuc.lua

 local filters = require 'util.filters';
 
 local util = module:require 'util';
+local ends_with = util.ends_with;
 local is_vpaas = util.is_vpaas;
 local room_jid_match_rewrite = util.room_jid_match_rewrite;
 local get_room_from_jid = util.get_room_from_jid;
         process_host(name);
     end
 end
+-- if the message received ends with the main domain, these are system messages
+-- for visitors, let's correct the room name there
+local function message_handler(event)
+    local origin, stanza = event.origin, event.stanza;
+
+    if ends_with(stanza.attr.from, main_domain) then
+        stanza.attr.from = stanza.attr.from:sub(1, -(main_domain:len() + 1))..local_domain;
+    end
+end
+
 process_host_module(local_domain, function(host_module, host)
     host_module:hook('iq/host', stanza_handler, 10);
+    host_module:hook('message/full', message_handler);
 end);
 
 -- only live chat is supported for visitors