Receive HiveError on HiveImpl.openLazyBox

**Steps to Reproduce**
Receive error `HiveError: This should not happen. Please open an issue on GitHub.`

Stack Trace:
```
File "binary_reader_impl.dart", line 249, in BinaryReaderImpl.readFrame
File "frame_io_helper.dart", line 72, in _KeyReader.readKeys
File "frame_io_helper.dart", line 31, in FrameIoHelper.keysFromFile
File "storage_backend_vm.dart", line 84, in StorageBackendVm.initialize
File "hive_impl.dart", line 106, in HiveImpl._openBox
File "hive_impl.dart", line 152, in HiveImpl.openLazyBox
```

**Code sample**
Variable `storeType` is enum. Variable `basePath` is path to documents directory on iOS and Android.

```
String get storeName => _storeName ??= storeType.toString().split('.')[1];
...
box = await Hive.openLazyBox(storeName, path: basePath);
```

**Version**
- Platform: iOS, Android
- Flutter version: 1.22.5
- Hive version: 1.4.1+1

Start with the stack trace at binary_reader_impl.dart line 249, then follow the key-reading path through frame_io_helper.dart, storage_backend_vm.dart, and hive_impl.dart. Reproduce the failure with the supplied openLazyBox sample on the stated platforms and versions; done means the reported HiveError is explained and the affected opening path behaves correctly.

Written by the indexing model from the issue text.