fix bug https://github.com/Neilpang/acme.sh/issues/2695

fix bug https://github.com/Neilpang/acme.sh/issues/2695
If a domain was already verified by http-01 method,  when we try to issue a cert for them same domain with dns-01 method, we just get only one challenge object of type http-01 with "valid" status, from the authz-v3 url. So, we report error that we are not able the validate the domain, because of that we don't find dns-01 challenge.
This behavior is not the same as before. I believe it was changed by the letsencrypt CA.