Table: not display tooltip when cell is empty (#13152)

* Update table-body.js

* Update table-body.js

packages/table/src/table-body.js

@@ -314,7 +314,7 @@ export default {
 
       // 判断是否text-overflow, 如果是就显示tooltip
       const cellChild = event.target.querySelector('.cell');
-      if (!hasClass(cellChild, 'el-tooltip')) {
+      if (!(hasClass(cellChild, 'el-tooltip') && cellChild.childNodes.length)) {
         return;
       }
       // use range width instead of scrollWidth to determine whether the text is overflowing