Click on search icon shall put focus in input when input is empty

Fixes https://community.openproject.com/wp/29636

frontend/src/app/modules/global_search/global-search-input.component.ts

@@ -137,6 +137,8 @@ export class GlobalSearchInputComponent implements OnInit, OnDestroy {
         this.toggleMobileSearch();
         // open ng-select menu on default
         jQuery('.ng-input input').focus();
+      } else if (this.ngSelectComponent.filterValue.length === 0) {
+        this.ngSelectComponent.focus();
       } else {
         this.submitNonEmptySearch();
       }