CRUD导出 Excel 模板，暂无数据，在文档示例中就有问题

#### 描述问题：

在你们自己组件文档中就有问题，点击导出excel模板，报暂无数据错误

#### 截图或视频：

#### 如何复现（请务必完整填写下面内容）：

1. 你是如何使用 amis 的？
`sdk`、`npm` 或`其他`...

2. amis 版本是什么？请先在最新 beta 版本测试问题是否存在

3. 粘贴有问题的完整 `amis schema` 代码：
{
"type": "page",
"body": {
"type": "crud",
"syncLocation": false,
"headerToolbar": [
{
"type": "export-excel-template",
"label": "导出 Excel 模板"
}
],
"columns": [
{
"name": "id",
"label": "ID"
},
{
"name": "engine",
"label": "Rendering engine"
},
{
"name": "browser",
"label": "Browser"
},
{
"name": "platform",
"label": "Platform(s)"
},
{
"name": "version",
"label": "Engine version"
},
{
"name": "grade",
"label": "CSS grade"
}
]
}
}

4. 操作步骤
请简单描述一下复现的操作步骤...

Start with the documented CRUD example and the supplied schema, then reproduce the export-excel-template action with no CRUD data. Trace the export behavior from that example and verify that exporting an empty template completes without the “暂无数据” error.

Written by the indexing model from the issue text.