Hide BottomNavigationBar when document have just one page.

[ThiagoBfim]

I Had some problemens when i tried to use a pdf with just one page.
I want to hide BottomNavigationBar, but it's impossible.

Code with error:

`void main() => runApp(MyApp());

class MyApp extends StatefulWidget {
@OverRide
_MyAppState createState() => _MyAppState();
}

class _MyAppState extends State {
bool _isLoading = true;
PDFDocument document;

@OverRide
void initState() {
super.initState();
loadDocument();
}

loadDocument() async {
document = await PDFDocument.fromURL('https://www.w3.org/WAI/ER/tests/xhtml/testfiles/resources/pdf/dummy.pdf');
setState(() => _isLoading = false);
}

@OverRide
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(
title: const Text('FlutterPluginPDFViewer'),
),
body: Center(
child: _isLoading
? Center(child: CircularProgressIndicator())
: PDFViewer(document: document, showNavigation: false,)),
),
);
}
}
`