Fix warning when the IRC mod isn't installed

init.lua

@@ -1,18 +1,18 @@
 -- Reboot mod for Minetest
 -- Waits for the last player to leave then shuts the server down
+--
 -- Copyright © 2018 by luk3yx
+--
 -- Permission is hereby granted, free of charge, to any person obtaining a copy
 -- of this software and associated documentation files (the "Software"), to deal
 -- in the Software without restriction, including without limitation the rights
 -- to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 -- copies of the Software, and to permit persons to whom the Software is
 -- furnished to do so, subject to the following conditions:
+--
 -- The above copyright notice and this permission notice shall be included in
 -- all copies or substantial portions of the Software.
+--
 -- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 -- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 -- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
@@ -28,7 +28,9 @@ local checkReboot
 checkReboot = function()
     if reboot and next(minetest.get_connected_players()) == nil then
         -- Time to reboot
-        if irc then irc.say("The server is empty! Rebooting...") end
+        if minetest.global_exists('irc') then
+            irc.say("The server is empty! Rebooting...")
+        end
         minetest.request_shutdown("Rebooting...", true, 1)
     end
 end