src: return undefined when validation err == 0

Extracted from the QUIC PR. Not specific to QUIC even if the
behavior is currently only used there.

Signed-off-by: James M Snell <jasnell@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/33107


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>