Gracefully free a NULL HANDSHAKE_RESULT

Reviewed-by: Rich Salz <rsalz@openssl.org>
diff --git a/test/handshake_helper.c b/test/handshake_helper.c
index ce530c2..3e7f129 100644
--- a/test/handshake_helper.c
+++ b/test/handshake_helper.c
@@ -25,6 +25,8 @@
 
 void HANDSHAKE_RESULT_free(HANDSHAKE_RESULT *result)
 {
+    if (result == NULL)
+        return;
     OPENSSL_free(result->client_npn_negotiated);
     OPENSSL_free(result->server_npn_negotiated);
     OPENSSL_free(result->client_alpn_negotiated);