Ticket #47660 - config_set_allowed_to_delete_attrs: Valgrind reports Invalid read
    
    Description: There was a logic error in checking the availability of
    a pointer.  Before checking the contents of an address, the correctness
    of the pointer needed to be checked.
    
    Also, one memory leak was found in the error return case.
    
    Note: these 2 issues were introduece by this commit:
    commit 94b123780b21e503b78bceca9d60904206ef91fa
    Trac Ticket #447 - Possible to add invalid attribute to nsslapd-allowed-to-delete-attrs
    
    https://fedorahosted.org/389/ticket/47660
    
    Reviewed by rmeggins@redhat.com (Thank you, Rich!)