CLDAP: Return empty reply on non-fatal errors
    
    Windows DCs return an empty reply when a legal request cannot satisfied.
    If we get EINVAL or ENOENT it means the information requested could not be
    found or input parameters were bogus.
    Always return an empty reply in these cases.
    
    On any other internal error just return, the request may have been legit but we
    can't really handle it right now, pretend we never saw it and hope the next
    attempt will succeed.
    
    Fixes: https://fedorahosted.org/freeipa/ticket/3639
    
    Signed-off-by: Simo Sorce <simo@redhat.com>