Don't add the first pkcs12 certificate multiple times

Don't add the first pkcs12 certificate multiple times

This fixes a regression introduced by commit 1d6c867. When exporting a set
of certificates to a PKCS12 file we shouldn't add the first one twice. Also
we restore historic behaviour with respect to the canames option where we
have no ee certificate with key.

Fixes #15983

Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16001)