Don't Encrypt if only one Column is Found

[alexanderkiel]

It makes no sense to encrypt CSV files with only one column, because we wouldn't do anything. Succeeding with that noop encryption is dangerous, because one could output sensitive data unencrypted. We had the case were the columns were quoted in a weird way so that it looked like a one column file to csv-crypt, but in fact there ware columns with sensitive data outputted in cleartext.