Ticket 48858 - Segfault changing nsslapd-rootpw
    
    Bug Description:  py.ldap has a bug where it will send empty change lists. This
    trigged a segfault in Directory Server where hash_rootpw expected there to be
    at least a single value to act upon
    
    Fix Description:  Check that mod_bvalues is not NULL
    
    https://fedorahosted.org/389/ticket/48858
    
    Author: wibrown
    
    Review by: nhosoi (Thank you!)