role sync doesn't subscribe when adding role

I'm testing the new role sync feature and noticed that adding a role did not subscribe the user to the list. This is happening in user_mailman_register_user in the update case. The variable $allow_new_role is being initialized outside the loop that iterates over the list. Therefore the call to _user_mailman_register_allowed_list() is being called with a null list.

Patch attached.