chore: use explicit !== undefined check instead of truthy check (@ennajari) (#7805)

## Summary

- Use explicit `!== undefined` check instead of truthy check for cached
`Promise` in memoize utility (`json-data.ts`)

## Test plan

- [ ] Memoized async functions cache correctly

Author: ennajari

.gitignore

@@ -132,4 +132,4 @@ frontend/static/webfonts-preview
 .turbo
 frontend/.env.sentry-build-plugin
 .claude/worktrees
-1024MiB
+1024MiB

frontend/src/ts/utils/json-data.ts

@@ -52,7 +52,7 @@ export function memoizeAsync<P, Args extends unknown[], R>(
     const key = getKey ? getKey(...args) : (args[0] as P);
 
     const cached = cache.get(key);
-    if (cached) {
+    if (cached !== undefined) {
       return cached;
     }