JsonCacheInfoRepository: FormatException: Unexpected end of input (at character 1) ^

## 🐛 Bug Report

occasionally this error is generated when initializing CacheManager with JsonCacheInfoRepository

```
Fatal Exception: io.flutter.plugins.firebase.crashlytics.FlutterError: FormatException: Unexpected end of input (at character 1)

^

at .jsonDecode(dart:convert)
at JsonCacheInfoRepository._readFile(json_cache_info_repository.dart:143)
at JsonCacheInfoRepository.open(json_cache_info_repository.dart:40)
at new CacheStore.(cache_store.dart:34)
```

This happens when the {databaseName}.json file is created but empty and jsonString = ""

```
JsonCacheInfoRepository.dart: _readFile()
final json = jsonDecode(jsonString) as List;
```
A possible solution would be to check that the file is not empty before decoding the json

```
if (await file.exists() && await file.length() > 0) {
try {
final jsonString = await file.readAsString();
final json = jsonDecode(jsonString) as List;
```

> note: I don't know why the json file is empty and not with an empty list []

### Expected behavior

no error

### Configuration

Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel stable, 3.16.1, on Microsoft Windows [Versi¢n 10.0.22631.3296], locale es-CL)
[√] Windows Version (Installed version of Windows is version 10 or higher)
[√] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
[√] Chrome - develop for the web
[√] Visual Studio - develop Windows apps (Visual Studio Build Tools 2022 17.8.2)
[√] Android Studio (version 2022.3)
[√] VS Code (version 1.87.2)
[√] Connected device (4 available)
[√] Network resources

• No issues found!

**Version:** 3.3.1

**Platform:**
- [ ] :iphone: iOS
- [x] :robot: Android 13 (AP I33)

json_cache_info_repository.dart の JsonCacheInfoRepository._readFile（143 行目付近）から始め、空のデータベース JSON ファイルがどのように jsonDecode に渡されるかを調べてください。空ファイルのケースを再現するかカバーし、その後、通常の JSON の読み込みを維持したまま、FormatException なしで初期化が完了することを確認してください。

索引モデルが issue の本文から書いたものです。