Fix error when deleting a pinned row (#12311)

* fix(tree-grid): fix error when deleting a pinned row

* refactor(tree-grid): add missing semicolon

* fix(tree-grid): add requested changes

Author: MonikaKirkova

projects/igniteui-angular/src/lib/grids/tree-grid/tree-grid-integration.spec.ts

@@ -1762,5 +1762,20 @@ describe('IgxTreeGrid - Integration #tGrid', () => {
             firstRow.pinned = true;
             expect(firstRow.pinned).toBeTrue();
         });
+
+        it('should delete pinned row without errors', () => {
+            treeGrid.pinRow(147);
+            fix.detectChanges();
+            const firstRow = treeGrid.pinnedRows[0];
+
+            expect(firstRow.isRoot).toBe(true);
+            expect(firstRow.pinned).toBeTrue();
+            expect(firstRow.data.ID).toEqual(147);
+
+            treeGrid.deleteRowById(147);
+            fix.detectChanges();
+
+            expect(firstRow.isRoot).toBe(false);
+        });
     });
 });

projects/igniteui-angular/src/lib/grids/tree-grid/tree-grid-row.component.ts

@@ -73,7 +73,7 @@ export class IgxTreeGridRowComponent extends IgxRowDirective implements DoCheck
         if (isPinnedArea) {
             treeRec = this.grid.unpinnedRecords.find(x => x.data === this.data);
         }
-        return treeRec.level === 0;
+        return treeRec?.level === 0;
     }
 
     /**