uni-app pickerview显示异常，小程序显示正常

uni-app pickerview显示异常，小程序显示正常

产品分类：uniapp/H5

浏览器平台：Chrome
浏览器版本：95.0.4638.69

### 示例代码：
```vue
<template>
<view class="container">  
    <view class="diygw-form-item diygw-col-24">  
        <view class="title">标题</view>  
        <view class="input">  
            <picker mode="multiSelector" @columnchange="changePickers" :value="pickersIndex" :range="pickersDatas">  
                <view class="uni-input">  
                    {{ pickersDatas[0][pickersIndex[0]] }},  
                </view>  
            </picker>  
        </view>  
    </view>  
</view>  
</template>  

<script>
//create by: 邓志锋 280160522@qq.com http://www.diygw.com
export default {
data() {
return {
input2: '',
date1: '',
pickersInitDatas: [{
"children": [{
"children": [{
"children": [],
"text": "无锡市"
}, {
"children": [],
"text": "深圳市"
}],
"text": "广州市"
}, {
"children": [{
"children": [],
"text": "梅州市"
}],
"text": "中山市"
}],
"text": "广东省"
}, {
"children": [],
"text": "江苏省"
}],
pickersDatas: [
['广东省', '江苏省'],
['广州市', '中山市'],
['无锡市', '深圳市']
],
pickersIndex: [0, 0, 0]
}
},
onShareAppMessage: function() {},
onLoad(option) {
if (option) {
this.setData({
globalOption: option
})
}
},
mounted() {
this.init();
},
methods: {
async init() {

},
getPickerChildren1(data,chindInex1,childIndex2){
     if(chindInex1!=null && data[chindInex1] && data[chindInex1].children && data[chindInex1].children){
         let children = data[chindInex1].children
         //只判断一级
         if(childIndex2==null){
             if(children!=null && children.length>0){
                return children.map(item=>item.text)
             }else{
                 return []
             }
         }else{
             //判断二级
             //有可能并设置下级结点
             if(children[childIndex2]==null){
                 return []
             }
             let children2 = children[childIndex2].children
             if(children2!=null && children2.length>0){
                return children2.map(item=>item.text)
             }else{
                return []
             }
         }
     }else{
         return []
     }

},
changePickers(evt) {
this.pickersIndex[evt.detail.column] = evt.detail.value
if (evt.detail.column == 0) {
    this.pickersIndex.splice(1, 1, 0)
    this.pickersIndex.splice(2, 1, 0)
    this.pickersDatas[1] = this.getPickerChildren1(this.pickersInitDatas,this.pickersIndex[0],null)
    this.pickersDatas[2] = this.getPickerChildren1(this.pickersInitDatas,this.pickersIndex[0],0)

}else if (evt.detail.column == 1) {
    this.pickersDatas[2] = this.getPickerChildren1(this.pickersInitDatas,this.pickersIndex[0],this.pickersIndex[1])
    this.pickersIndex.splice(2, 1, 0)
}
this.$forceUpdate()
}
}
</script>  

<style lang="scss"></style>  

操作步骤：

就是拖动省份至江苏省，显示空是正常的，再拖回广东省时显示异常。

预期结果：

就是拖动省份至江苏省，显示空是正常的，再拖回广东省时显示异常，数据本身都是已经0 0 0。

实际结果：

显示上异常，显示上都自动至底部显示，不正确

bug描述：

pickerview因为可能某些子节点缺失的情况下，滑动后有些节点不会变化