WebView in TabBarView show not correct.

还没有人认领这个 Issue。

```
class DetailAcademicPage extends StatelessWidget {
final String title;
DetailAcademicPage(this.type);

@override
Widget build(BuildContext context) {
final SectionPage tab1 = SectionPage(0, title);
final SectionPage tab2 = SectionPage(1, title);
final SectionPage tab3 = SectionPage(2, title);
return Scaffold(
body: DefaultTabController(
length: 3,
child: Scaffold(
backgroundColor: Colors.white,
appBar: AppBar(
title: Text(
title,
style: TextStyle(color: Colors.white),
),
centerTitle: true,
iconTheme: IconThemeData(color: Colors.white),
bottom: TabBar(
indicatorColor: Colors.white,
tabs: [
Tab(
child: Text("Section 1")),
Tab(
child: Text("Section 2")),
Tab(
child: Text("Section 3",))
])),
body: TabBarView(
physics: NeverScrollableScrollPhysics(),
children: [tab1, tab2, tab3],
),
)),
);
}
}

class SectionPage extends StatefulWidget {
final int pageNumber;
final String title;

SectionPage(this.pageNumber, this.title);

@override
State createState() {
return _SectionPage();
}
}

class _SectionPage extends State with AutomaticKeepAliveClientMixin {
String urlPath;

@override
void initState() {
super.initState();
switch (widget.pageNumber) {
case 0:
urlPath = "/Section 1.html";
break;
case 1:
urlPath = "/Section 2.html";
break;
case 2:
urlPath = "/Section 3.html";
break;

}
}

@override
Widget build(BuildContext context) {
super.build(context);
return Container(
child: WebviewScaffold(
url: urlPath,
resizeToAvoidBottomInset: false,
withJavascript: true,
withZoom: false,
withLocalStorage: true,
scrollBar: false,
supportMultipleWindows: false,
hidden: true),
);
}

@override
bool get wantKeepAlive => true;
}

```

## Steps to Reproduce

I create TabBar with 3 TabBarView, every TabBarView i use WebView inside.
But when render webview it auto put appbar top and can't scroll, and bottom view empty.

## Logs
- I dont see error log in Logcat

```
```

```
```

Start by reproducing the provided DetailAcademicPage, TabBarView, and WebviewScaffold example in a minimal Flutter app, then inspect the plugin's WebView layout and scrolling behavior. The issue is resolved when each tab's WebView is positioned below the app bar, the lower view is not empty, and its content scrolls correctly.

由索引模型根据 Issue 内容生成。