Generated `messages` virtual file contains syntax error when some locale files written in yaml is empty

### Reporting a bug?

Generated `messages` virtual file contains syntax error when some locale files written in yaml is empty

### Expected behavior

Should not contain syntax errors.

### Reproduction

Unable to create a "minimal" one now, but soon

But it should be pretty straight-forward to reproduce using such configuration: [vite.config.ts](https://github.com/so1ve/openbmclapi-dashboard/blob/main/vite.config.ts)

### Issue Package

unplugin-vue-i18n

### System Info

```shell
Unable to run the command now - will update later using my PC
```

### Screenshot

_No response_

### Additional context

_No response_

### Validations

- [X] Read the [Contributing Guidelines](https://github.com/intlify/bundle-tools/blob/main/.github/contributing.md).
- [X] Read the README
- [X] Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
- [X] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/intlify/bundle-tools/discussions).