chore(*): Add null check.

Author: MKirova

projects/igniteui-angular/src/lib/grids/row.directive.ts

@@ -524,7 +524,7 @@ export class IgxRowDirective implements DoCheck, AfterViewInit, OnDestroy {
 
     public isCellActive(visibleColumnIndex) {
         const node = this.grid.navigation.activeNode;
-        const field = this.grid.visibleColumns[visibleColumnIndex].field;
+        const field = this.grid.visibleColumns[visibleColumnIndex]?.field;
         const rowSpan = this.metaData?.cellMergeMeta?.get(field)?.rowSpan;
         if (rowSpan > 1) {
             return node ? (node.row >= this.index && node.row < this.index + rowSpan)