auto_profiles.lua: actually exit when no auto profiles are defined

Unsetting _G.mp_event_loop at the top level quits the script, but not
within callbacks. Use the new exit() function instead. Fixes e2284fba18.

This actually has an edge case since e2284fba18 where you can add auto
profiles only later with load-config-file and the script stays unloaded,
but it's still reasonable to quit if mpv.conf has no conditional
profiles. You could always explicitly set --load-auto-profiles=yes in
this case.

player/lua/auto_profiles.lua

@@ -194,8 +194,7 @@ mp.observe_property("profile-list", "native", function (_, profiles_property)
     load_profiles(profiles_property)
 
     if #profiles < 1 and mp.get_property("load-auto-profiles") == "auto" then
-        -- make it exit immediately
-        _G.mp_event_loop = function() end
+        exit()
         return
     end