[TD-6167]<fix> fix memory leak

src/client/src/tscPrepare.c

@@ -1503,6 +1503,14 @@ TAOS_STMT* taos_stmt_init(TAOS* taos) {
     return NULL;
   }
 
+  if (TSDB_CODE_SUCCESS != tscAllocPayload(&pSql->cmd, TSDB_DEFAULT_PAYLOAD_SIZE)) {
+    free(pSql);
+    free(pStmt);
+    terrno = TSDB_CODE_TSC_OUT_OF_MEMORY;
+    tscError("failed to malloc payload buffer");
+    return NULL;
+  }
+
   tsem_init(&pSql->rspSem, 0, 0);
   pSql->signature = pSql;
   pSql->pTscObj   = pObj;