scroll上拉加载问题

### Version
1.12.38

### Reproduction link
[https://approval.myoas.com](https://approval.myoas.com)

### Steps to reproduce
1.上拉到底部不能加载更多了
2.滑到顶部下拉刷新
3.再向下滚动不会触发滚动加载@pulling-down

### What is expected?
1.上拉到底部不能加载更多了
2.滑到顶部下拉刷新
3.再向下滚动触发滚动加载@pulling-down

### What is actually happening?
1.上拉到底部不能加载更多了
2.滑到顶部下拉刷新
3.再向下滚动没有触发滚动加载@pulling-down

### Dependencies Version
vue: 2.6.11
better-scroll: 2.0.3

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地址访问需要权限，按照步骤很容易复现，希望修复