DataTable VirtualScroll alignment issue

[konradkoc]

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[X ] bug report
[ ] feature request
[ ] support request => Please do not submit support request here, instead see https://forum.primefaces.org/viewforum.php?f=57

Current behavior

1. When scrolling DataTable from bottom to top, virtualScroll encounters error and doesnt render any data. When inspecting the issue it seems like when event onScrollIndexChange triggers, the bug happens when e.first < 0. When I go on with scrolling to top it fixes and e.first === 0
2. VirtualSroll content seems to be translated of virtual row size. But in my case, the header is much bigger than row size which makes the first row of dataTable not fully visible.

Expected behavior

1. When for some reason e.first < 0 -> just use 0 with proper index shift.
2. Use header size to translate virtualScroll content.

Minimal reproduction of the problem with instructions

Please tell us about your environment:

• React version:
  7.0.1

• PrimeReact version:
  7.0.0

• Browser: [all | Chrome XX | Firefox XX | IE XX | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]

• Language: [all | TypeScript X.X | ES6/7 | ES5]