free NULL cleanup

EVP_.*free; this gets:
        EVP_CIPHER_CTX_free EVP_PKEY_CTX_free EVP_PKEY_asn1_free
        EVP_PKEY_asn1_set_free EVP_PKEY_free EVP_PKEY_free_it
        EVP_PKEY_meth_free; and also EVP_CIPHER_CTX_cleanup

Reviewed-by: Kurt Roeckx <kurt@openssl.org>