nixos/luks: allow empty passphrases in prompt (#491473)

                      # and try reading it from /dev/console with a timeout

                      IFS= read -t 1 -r passphrase

                      if [ -n "$passphrase" ]; then

                      if [ $? = 0 ]; then

                         ${

                           if luks.reusePassphrases then

                             ''

                  fi

              done

              echo -n "Verifying passphrase for ${dev.device}..."

              echo -n "$passphrase" | ${csopen} --key-file=-

              echo "$passphrase" | ${csopen}

              if [ $? == 0 ]; then

                  echo " - success"

                  ${