openssl: Fix memory leak when verifying plain RSA signatures with old BoringSSL versions

Fixes: 21b586c61c ("openssl: Fixes for RSA with OpenSSL 3.0")

src/libstrongswan/plugins/openssl/openssl_rsa_public_key.c

@@ -156,9 +156,9 @@ static bool verify_plain_signature(private_openssl_rsa_public_key_t *this,
 	{
 		valid = chunk_equals_const(data, chunk_create(buf, len));
 	}
-	free(buf);
 	EVP_PKEY_CTX_free(ctx);
 #endif
+	free(buf);
 	return valid;
 }