fix: 修复树结构children为空并且开启default-expand-all导致计算高度问题

[wangdaodao]

具体示例：

<template>
  <div>
    <el-alert type="warning" title="非懒加载的树结构需要写成懒加载的形式，否则树展开后，来回滚动会导致展开树重置为未展开状态" show-icon></el-alert>
    <virtual-scroll
      ref="virtualScroll"
      :data="list"
      :item-size="62"
      key-prop="id"
      @change="virtualList => (tableData = virtualList)">
      <el-table
        v-loading="loading"
        :data="tableData"
        default-expand-all
        height="500px"
        style="width: 100%"
        row-key="id"
        border
        lazy
        :load="(tree, treeNode, resolve) => resolve(tree.children)"
        :tree-props="{hasChildren: 'children'}">
        <el-table-column label="id" prop="id"></el-table-column>
        <el-table-column label="内容" prop="text"></el-table-column>
        <el-table-column label="内容省略" prop="text" show-overflow-tooltip></el-table-column>
      </el-table>
    </virtual-scroll>
  </div>
</template>

<script>
import VirtualScroll from 'el-table-virtual-scroll'

export default {
  components: {
    VirtualScroll
  },
  data () {
    return {
      loading: false,
      list: [],
      tableData: []
    }
  },
  methods: {
    fetchData () {
      this.loading = true
      this.list = []
      setTimeout(() => {
        this.list = []
        for (let i = 1; i < 2000; i++) {
          const text = this.getRandomContent()
          const text2 = this.getRandomContent()
          this.list.push({
            id: i,
            show: false,
            text,
            text2,
            children: []
          })
        }
        this.loading = false
      }, 1000)
    },
    getRandomContent () {
      const content = [
        '这是一条测试数据',
        '君不见黄河之水天上来，奔流到海不复回。',
        '十年生死两茫茫',
        '寻寻觅觅，冷冷清清，凄凄惨惨戚戚。',
        '桃花坞里桃花庵，桃花庵里桃花仙；桃花仙人种桃树，又摘桃花卖酒钱。',
        '明月几时有，把酒问青天。',
        '槛菊愁烟兰泣露，罗幕轻寒，',
        '寒蝉凄切，对长亭晚，骤雨初歇。都门帐饮无绪，留恋处，兰舟催发。执手相看泪眼，竟无语凝噎。念去去，千里烟波，暮霭沉沉楚天阔。多情自古伤离别，更那堪冷落清秋节！今宵酒醒何处？杨柳岸，晓风残月。此去经年，应是良辰好景虚设。便纵有千种风情，更与何人说？',
        '红豆生南国，春来发几枝。',
        '黄鹂'
      ]
      const i = Math.floor(Math.random() * 10)
      return content[i]
    }
  },
  created () {
    this.fetchData()
  }
}
</script>

感谢作者开源组件，能让更多人方便使用。

另外感觉饿了么表格 default-expand-all 属性开启后，虚拟滚动会有问题。

[xiaocheng555]

ok，修复了

[xiaocheng555]

ok，修复了