crypto: avoid unitializing ECDH objects on error

The previous code changed the private key of the ECDH object, but
removed the public key if deriving it from the private key failed.
Instead, if deriving the public key fails, neither the private nor
the public key stored in the ECDH object should be updated.

PR-URL: https://github.com/nodejs/node/pull/34302


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>