Do not attempt to resolve nameless servers
    
    The failover code is not strictly in charge of resolving. Its main
    function is to provide a server to connect to for a service.
    
    It is legal, although not currently used, to have a server that has no
    name (server->common == NULL). In this case, no resolving should be done
    and it is assumed that the failover user, which are the SSSD back ends
    in our case, would perform any resolving out of band, perhaps using the
    user_data attribute of fo_server structure.