Dynamic scroller not handling correct position

### Describe the bug

elements are shown and overlap other items

### Reproduction

```js

export default {
computed: {
chatMsgList() {
let list = this.$store.state.chat.chatMsgList;
if (list.length > 200) {
const num = list.length - 200;
list.splice(0, num);
}
list = list.map((item, index) => {
return {
id: index++,
content: item
};
});
return list;
}
}
}

```

### System Info

```shell
"vue": "^2.5.17",
"vue-virtual-scroller": "^1.1.2",
```

### Used Package Manager

npm

### Validations

- [X] Read the [docs](https://github.com/Akryum/vue-virtual-scroller/blob/master/packages/vue-virtual-scroller/README.md).
- [X] Check that there isn't [already an issue](https://github.com/Akryum/vue-virtual-scroller/issues) that reports the same bug to avoid creating a duplicate.
- [X] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/Akryum/vue-virtual-scroller/discussions).
- [X] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.