WebView is not fullscreen

Hi there, i want just confirm is this a bug or not?
Maybe I'm doing something wrong? Or maybe this is a Xiaomi specific bug when renders webview widget.

red offset on the right and bottom.

[Screenschot](https://i.imgur.com/Ahab0yB.jpg)

in the UI is nothing special:
```
return MaterialApp(
home: Scaffold(
body: SafeArea(
child: WebviewScaffold(
url: initialUrl,
initialChild: Container(
color: Colors.red,
child: Center(
child: Text("Loading..."),
),
),
),
bottom: true,
left: true,
right: true,
top: true,
),
),
);
```

Thank you for help in advance =)

Start by reproducing the sample with WebviewScaffold on the reported Xiaomi device and compare its layout with the screenshot. Check whether the red offset comes from SafeArea, the scaffold's bottom/left/right/top settings, or the plugin's WebView rendering. Done means determining whether this is a plugin bug or an application layout issue.

Written by the indexing model from the issue text.