Fix a possible memory leak in sxnet_v2i

When a subsequent call to SXNET_add_id_asc fails
e.g. because user is a string larger than 64 char
or the zone is a duplicate zone id,
or the zone is not an integer,
a memory leak may be the result.

crypto/x509/v3_sxnet.c

@@ -103,8 +103,10 @@ static SXNET *sxnet_v2i(X509V3_EXT_METHOD *method, X509V3_CTX *ctx,
     int i;
     for (i = 0; i < sk_CONF_VALUE_num(nval); i++) {
         cnf = sk_CONF_VALUE_value(nval, i);
-        if (!SXNET_add_id_asc(&sx, cnf->name, cnf->value, -1))
+        if (!SXNET_add_id_asc(&sx, cnf->name, cnf->value, -1)) {
+            SXNET_free(sx);
             return NULL;
+	}
     }
     return sx;
 }