使用EasyRefresh+CustomScrollView+SliverToBoxAdapter时，若SliverToBoxAdapter内包含非固定高度的widget，header显示异常

[KaiLiDev]

使用EasyRefresh+CustomScrollView+SliverToBoxAdapter时，若SliverToBoxAdapter内包含非固定高度的widget，自定义的header显示异常；自定义Header是使用的ClassicHeader源码修改，下拉时只显示一个loading，完成之后显示文字；
`class _CusEasyRefreshState extends State {

@OverRide
Widget build(BuildContext context) {
return EasyRefresh(
onRefresh: widget.onRefresh,
onLoad: widget.onLoad,
header: _getClassicHeader(),
footer: _getFooter(),
child: CustomScrollView(
slivers: [
const HeaderLocator.sliver(),
if (widget.buildSliverToBoxAdapter != null)
SliverToBoxAdapter(
child: Expanded(child: widget.buildSliverToBoxAdapter!.call()??Container())),
widget.buildMainScrollWidget(),
const FooterLocator.sliver(),
],
),
);
}

_getClassicHeader() {
return const CusClassicHeader(
showMessage: false,
spacing: 0,
showText: true,
safeArea: false,
triggerOffset: 50,
maxOverOffset: 50,
position: IndicatorPosition.above,
mainAxisAlignment: MainAxisAlignment.center,
dragText: '',
armedText: '',
readyText: '',
processingText: '',
processedText: '已经加载全部',
noMoreText: '无更多数据',
failedText: '加载失败',
messageText: '上次更新 %T',
);
}

_getFooter() {
return ClassicFooter(
spacing: 0,
pullIconBuilder:
(BuildContext context, IndicatorState state, double animation) {
return Container();
},
// succeededIcon: null,
noMoreIcon: const SizedBox(),
failedIcon: const SizedBox(),
iconDimension: 0,
showMessage: false,
position: IndicatorPosition.locator,
dragText: '上拉加载',
armedText: '松手加载',
readyText: '正在加载...',
processingText: '正在加载...',
processedText: '已全部加载',
noMoreText: '已全部加载',
failedText: '加载失败',
messageText: '上次更新 %T',
);
}
}`

[KaiLiDev]

下拉异常时，loading框没了

[xuelongqy]

你把Expanded去掉试试看？