Wrong position of vertical custom scrollbar if horizontal scroll position was changed

Steps to Reproduce

run attached zul
scroll horizontally

Current Result

the position of the vertical scrollbar is wrong

Expected Result

the position of the vertical scrollbar is right

Debug Information

nativebar is okay

https://github.com/zkoss/zk/blob/v8.6.1/zul/src/archive/web/js/zul/Scrollbar.js#L287
Since the indicator is hidden, offsetWidth is 0

https://github.com/zkoss/zk/blob/v8.6.1/zul/src/archive/web/js/zul/Scrollbar.js#L767
needV is false

Workaround

1. Just avoid using custom scrollbar