Ticket 47525 - Don't modify preop entry in memberOf config
    
    We shouldn't be modifying the preop entry we fetch from the pblock
    when validating the memberOf config.  We currently apply the mods
    to it when performing validation for a modify operation, but we
    should be making a copy of the entry to use for validation instead.
    
    Modifying the preop entry directly can cause crashing in some cases.