不定高Item下拉加载，回滚位置不准确

[sa0012]

Describe

A clear and concise description of what the bug is.

To Reproduce

Steps to reproduce the behavior:

1. Click on '....'
2. Scroll down to '....'
3. See error

Reproduce demo

Providing a reproduce demo of this bug, that will help me solve the problem more quickly. You can fork by this online demo: https://codesandbox.io/s/live-demo-virtual-list-e1ww1

Other

• Version [e.g. 2.0]
• Browser [e.g. chrome, safari]

[ideagay]

did you reslove this bug?