else we get an error from this call, using a 16 byte (128 bit) nonce
is currently only supported by the still in draft
XChaCha20-Poly1305, not the current default specified by RFC 7539[0],
which uses a 12 byte (96 bit) nonce.
Fixes the following error:
> thread 'main' panicked at 'called `Result::unwrap()` on an `Err`
> value: ErrorStack([])', src/libcore/result.rs:1165:5
[0]: https://tools.ietf.org/html/rfc7539
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
