Ticket #47919 - ldbm_back_modify SLAPI_PLUGIN_BE_PRE_MODIFY_FN does not return even if one of the preop plugins fails.
    
    Bug Description: In ldbm_back_modify, if one of the be_preop plugins
    called at SLAPI_PLUGIN_BE_PRE_MODIFY_FN fail, ldbm_back_modify does
    not return there but go to the real modify operation.
    
    Fix Description: If an error is returned from be_preop plugins in
    ldbm_back_modify, it returns the error there and does not proceed
    the modify operation.
    
    https://fedorahosted.org/389/ticket/47919
    
    Reviewed by mreynolds@redhat.com (Thank you, Mark!!)