Fix a null access with encryption+UDP

[Hywan]

Will fix #9.

[Hywan]

Asking the review of @Pierozi in particular.

[Pierozi]

How you used UDP with Encryption ?
On my MWE, your PR still pass my test in tcp mode.
but udp does not work, and has never work.

[Hywan]

@Pierozi It does not work because we don't have nodes, since we use nodes with select + accept and we can't accept a UDP socket.

I propose to merge my PR: it removes a null access. Then, we open a new issue to support nodes (and therefore encryption) for UDP.

Thoughts?

[Pierozi]

👍 Yes, do it that.