Group cell of second level grouping unexpectedly render `null` in virtualTable, when only one row

[torrac12]

• [x] I have searched this repository's issues and believe that this is not a duplicate.

I'm using ...

• [x] React Grid
• [ ] React Chart
• [ ] React Scheduler

Current Behaviour

When drag horizontal scrollbar to right, second grouping level's group cell unexpected destroy in virtual table

Expected Behaviour

The second grouping level's group cell should persist.

Steps to Reproduce

examples on CodeSandbox

1. Resizing browser window to small size (to ensure the left most column will get collapsed when scrolling)
2. Expand the first level grouping row
3. Drag the horizontal scrollbar of virtualTable to right

Screenshots

This is right when app mounted

When drag scrollbar, the second grouping level's group cell unexpectedly render null, which cause total number of td tag less than we wanted. If there are multiple rows, the issue won't re-produce

Environment

• devextreme-reactive: 2.7.6

This may relate to the calculation of rowSpanBoundaries