Fix EVP todata and fromdata when used with selection of EVP_PKEY_PUBLIC_KEY.

Fix EVP todata and fromdata when used with selection of EVP_PKEY_PUBLIC_KEY.

The private key for rsa, dsa, dh and ecx was being included when the
selector was just the public key. (ec was working correctly).
This matches the documented behaviour.

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17200)