fix(Toolbar): Set isExporting & showProgress to false on exportStarted cancel.

Author: gedinakova

projects/igniteui-angular/src/lib/grids/toolbar/grid-toolbar-exporter.component.ts

@@ -130,6 +130,8 @@ export class IgxGridToolbarExporterComponent extends BaseToolbarDirective {
         this.toolbar.showProgress = true;
 
         if (args.cancel) {
+            this.isExporting = false;
+            this.toolbar.showProgress = false;
             return;
         }