Fix STOR of zero length files to ProFTPd with TLS
Fix STOR of zero length files to ProFTPd with TLS

Before this change, uploading a zero length file via TLS meant that
the tls.Handshake function was never called.

ProFTPd quite properly refuses to accept an empty TCP connection with
no TLS handshake as a zero length upload and gives the error

    425 Unable to build data connection: Operation not

See: https://forum.rclone.org/t/rclone-ftps-explicit-rclone-touch-empty-files-proftpd-unable-to-build-data-connection-operation-not-permitted/22522

jlaffaye/ftp