Extend EVP_PKEY_copy_parameters()

Make EVP_PKEY_copy_parameters() work if the destination has no type
(e.g. if obtained from EVP_PKEY_new()) or the underlying key is NULL.
This is useful where we want to copy the parameters from an existing
key to a new key.

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>