Ticket 47528 - 389-ds-base built with mozldap can crash from invalid free
    
    Bug Description:  The issue is that the slapi_escape_filter_value() returned string gets
                      freed by the caller. When using mozldap, this function can return the
                      original filter pointer, which can lead to a double free.
    
    Fix Description:  Return a copy of the filter str so it can be safely freed.  Also free
                      the buf if it's not being returned.
    
    https://fedorahosted.org/389/ticket/47528
    
    Reviewed by: nhosoi(Thanks!)
    (cherry picked from commit da59cff5e6d27c18bbb02cba98bb99c1bfa37c70)