files reset when state change

## Environment

**Package version:**
form_builder_file_picker: ^2.3.0

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```
```

Code sample

```
if (type == 'filepicker') {
return FormBuilderFilePicker(
name: 'filepicker_datum$page',
validator: FormBuilderValidators.required(errorText: 'Jawaban wajib diisi!'),
decoration: const InputDecoration(labelText: 'Attachments'),
maxFiles: 1,
previewImages: true,
onChanged: (val) {},
typeSelectors: [
TypeSelector(
type: FileType.any,
selector: Row(
children: const [
Icon(Icons.attachment),
Gap(8),
Text('Pilih Berkas'),
],
),
)
],
onFileLoading: (val) {
debugPrint(val.toString());
},
onSaved: (newValue) {},
// customFileViewerBuilder: customFileViewerBuilder,
);
}
```

## Description
i am using pageview, when finished fetching files, the list of files that have been fetxhed is reset to null.

**Expected behavior:**
file lists persists

**Current behavior:**
files reset

## Video

https://user-images.githubusercontent.com/111847308/218387741-ac248f22-27d7-434b-8350-d2bc41b6a46b.mp4