An `ftp://` transfer configured with `CURLUSESSL_NONE` can reuse a pooled FTP control connection that a previous easy handle upgraded with `

An ftp:// transfer configured with CURLUSESSL_NONE can reuse a pooled FTP
control connection that a previous easy handle upgraded with STARTTLS and
authenticated using a client certificate. The second handle performs neither a
new TLS handshake nor a new FTP login, so the server continues to authorize it
under the first handle's certificate identity.