idviews: clear intermediate target DN in all cases
    
    When processing a search request, slapi-nis attempts to detect an ID
    View lookup. A target DN is modified by extracting an ID view name. This
    temporary string is freed in the successful case but left unotouched if
    ID View wasn't requested. As a result, small leaks on each search
    request accumulate and a memory can get lost.
    
    Resolves: rhbz#1866113
    
    Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>