Sometimes vsftpd returns a 426 error when closing the stream even when
all the data has been transferred successfully. This is some TLS
protocol mismatch.
Rclone has code to deal with this already, but the error returned from
Close was wrapped in a multierror so the detection didn't work.
This properly extract `textproto.Error` from the errors returned by
`github.com/jlaffaye/ftp` in all the cases.
See: https://forum.rclone.org/t/vsftpd-vs-rclone-part-2/36774
0d8350d95d