fix(grid): address null TypeError on focusing a grid with no data and column headers - 20.1.x#16521

kacheshmarova merged 2 commits into20.1.xIgniteUI/igniteui-angular:20.1.xfrom

bpachilova/ariaHidden-header-groups-fix-16517-20.1.xIgniteUI/igniteui-angular:bpachilova/ariaHidden-header-groups-fix-16517-20.1.xCopy head branch name to clipboard