fix(Highlight): Check if the highlight group exists before activation. (#15762)

* test(Highlight): Adding a test for activating non-existent group.
* fix(Highlight): Adding a check for undefined before activation.

Author: gedinakova

projects/igniteui-angular/src/lib/directives/text-highlight/text-highlight.directive.spec.ts

@@ -299,6 +299,17 @@ describe('IgxHighlight', () => {
         expect(() => component.highlight.activateIfNecessary()).not.toThrowError();
     });
 
+    it('Should not throw when attempting to activate a non-existing group.', () => {
+        const fix = TestBed.createComponent(HighlightLoremIpsumComponent);
+        fix.detectChanges();
+
+        const component: HighlightLoremIpsumComponent = fix.debugElement.componentInstance;
+        component.highlightText('a');
+        component.groupName = 'test1';
+        fix.detectChanges();
+
+        expect(() => component.highlight.activateIfNecessary()).not.toThrowError();
+    });
 });
 
 @Component({

projects/igniteui-angular/src/lib/directives/text-highlight/text-highlight.directive.ts

@@ -318,7 +318,7 @@ export class IgxTextHighlightDirective implements AfterViewInit, AfterViewChecke
     public activateIfNecessary(): void {
         const group = this.service.highlightGroupsMap.get(this.groupName);
 
-        if (group.index >= 0 && group.column === this.column && group.row === this.row && compareMaps(this.metadata, group.metadata)) {
+        if (group && group.index >= 0 && group.column === this.column && group.row === this.row && compareMaps(this.metadata, group.metadata)) {
             this.activate(group.index);
         }
     }