[DSC-1486] feature: added check to main tab

Author: vNovski

src/app/item-page/cris-item-page-tab.resolver.ts

@@ -54,7 +54,11 @@ export class CrisItemPageTabResolver implements Resolve<RemoteData<PaginatedList
                 const givenTab = urlSplit[1];
                 const itemPageRoute = getItemPageRoute(itemRD.payload);
                 const isValidTab = tabsRD.payload.page.some((tab) => !givenTab || `/${tab.shortname}` === givenTab);
-                const mainTab = tabsRD.payload.page.filter((tab) => !tab.leading)[0];
+
+                const mainTab = tabsRD.payload.page.length === 1
+                  ? tabsRD.payload.page[0]
+                  : tabsRD.payload.page.find(tab => !tab.leading);
+
                 if (!isValidTab) {
                   // If wrong tab is given redirect to 404 page
                   this.router.navigateByUrl(getPageNotFoundRoute(), { skipLocationChange: true, replaceUrl: false });