ipa-kdb: get_authz_data_types() make sure entry can be NULL
    
    This function determines which type of authorization data should be
    added to the Kerberos ticket. There are global default and it is
    possible to configure this per service as well. The second argument is
    the data base entry of a service. If no service is given it makes sense
    to return the global defaults and most parts of get_authz_data_types()
    handle this case well and this patch fixes the remain issue and adds a
    test for this as well.
    
    Reviewed-By: Tomas Babej <tbabej@redhat.com>