fix: root dir will erasured when disableAsyncCache set

```typescript import { IndexedDB } from '@zenfs/dom'; import { resolveMountConfig, fs } from '@zenfs/core'; const mountConfig = await resolveMountConfig({ backend: IndexedDB, storeName: dbStoreName, disableAsyncCache: true, }); fs.mount(rootDir, mountConfig); ``` when set `disableAsyncCache: true` `await fs.readdir(rootDir)` always empty