option: fix option with idx 0 not working

src/app/core/data/search.service.ts

@@ -58,7 +58,7 @@ export class SearchService {
     return this.index.pipe(
       switchMap(index => {
         const idx = index ? index.get_idx_by_name(name) : undefined;
-        return idx ? this.getByIdx(idx) : of(undefined);
+        return typeof idx === "undefined" ? of(undefined) : this.getByIdx(idx);
       })
     );
   }