og promote role doesn't work in user registration process

Issue Summary

Hi all
i just try to promote a user while a registration process and it doesn't work
I had a look on the og_promote_og() function on line 39 where a switch seems proceed to the assignement depending hook_user() operation. case 'insert' is empty, so i think the bug is here but i'm not capable to fix it.

nb : sorry for my poor frenchy english !