Make sure that OpenID extensions don't return anything when not requested
    
    This makes sure that our OpenID extensions don't provide any responses if they were
    not requested, instead of providing empty responses.
    Some Relying Parties don't like to get responses for extensions they didn't ask for.
    
    Signed-off-by: Patrick Uiterwijk <puiterwijk@redhat.com>
    Reviewed-by: Pierre-Yves Chibon <pingou@pingoured.fr>