Offline data mode causes isFlutterApp to fail with `Null check operator used on a null value`

This code in connected_app.dart fails for connected controllers, when loading saved data:

```
Future get isFlutterApp async => _isFlutterApp ??=
await serviceManager!.libraryUriAvailable(flutterLibraryUri);
```

It is expected that connected controller should function as normal in offline data mode.