chore: code optimization

source/client/src/clientMain.c

@@ -121,14 +121,13 @@ TAOS *taos_connect(const char *ip, const char *user, const char *pass, const cha
 
 int taos_set_notify_cb(TAOS *taos, __taos_notify_fn_t *fp, void *param) {
   if (taos == NULL) {
-    return 0;
+    return TSDB_CODE_INVALID_PARA;
   }
 
   STscObj *pObj = acquireTscObj(*(int64_t *)taos);
   if (NULL == pObj) {
     tscError("invalid parameter for %s", __func__);
-    terrno = TSDB_CODE_TSC_DISCONNECTED;
-    return -1;
+    return TSDB_CODE_TSC_DISCONNECTED;
   }
 
   int32_t type = param ? *(int32_t *)param : 0;