配置了ScrollController之后滚动触发报错

[yiios]

原因是preIndexOffset的默认值是null，不能用于在package:flutter_section_table_view/flutter_section_table_view.dart:294:27 这个地方进行比较。

下面是日志
`flutter: The following NoSuchMethodError was thrown while dispatching notifications for ScrollController:
flutter: The method '>' was called on null.
flutter: Receiver: null
flutter: Tried calling: >(271.3333435058594)
flutter:
flutter: When the exception was thrown, this was the stack:
flutter: #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:50:5)
flutter: #1 double.< (dart:core-patch/double.dart:82:18)
flutter: #2 _SectionTableViewState.calculateIndexPathAndOffset. (package:flutter_section_table_view/flutter_section_table_view.dart:294:27)
flutter: #3 ChangeNotifier.notifyListeners (package:flutter/src/foundation/change_notifier.dart:206:21)
flutter: #4 ChangeNotifier.notifyListeners (package:flutter/src/foundation/change_notifier.dart:206:21)
flutter: #5 ScrollPosition.notifyListeners (package:flutter/src/widgets/scroll_position.dart:701:11)
flutter: #6 ScrollPosition.setPixels (package:flutter/src/widgets/scroll_position.dart:218:9)
flutter: #7 ScrollPositionWithSingleContext.setPixels (package:flutter/src/widgets/scroll_position_with_single_context.dart:83:18)
flutter: #8 ScrollPositionWithSingleContext.applyUserOffset (package:flutter/src/widgets/scroll_position_with_single_context.dart:126:5)
flutter: #9 ScrollDragController.update (package:flutter/src/widgets/scroll_activity.dart:372:14)
flutter: #10 ScrollableState._handleDragUpdate (package:flutter/src/widgets/scrollable.dart:498:12)
flutter: #11 DragGestureRecognizer._checkUpdate. (package:flutter/src/gestures/monodrag.dart:383:46)
flutter: #12 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
flutter: #13 DragGestureRecognizer._checkUpdate (package:flutter/src/gestures/monodrag.dart:383:7)
flutter: #14 DragGestureRecognizer.handleEvent (package:flutter/src/gestures/monodrag.dart:253:9)
flutter: #15 PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:75:13)
flutter: #16 PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:102:11)
flutter: #17 _WidgetsFlutterBinding&BindingBase&GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:218:19)
flutter: #18 _WidgetsFlutterBinding&BindingBase&GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:198:22)
flutter: #19 _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:156:7)
flutter: #20 _WidgetsFlutterBinding&BindingBase&GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:102:7)
flutter: #21 _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:86:7)
flutter: #25 _invoke1 (dart:ui/hooks.dart:250:10)
flutter: #26 _dispatchPointerDataPacket (dart:ui/hooks.dart:159:5)
flutter: (elided 3 frames from package dart:async)
flutter:
flutter: The ScrollController sending notification was:
flutter: ScrollController#a8730(one client, offset 271.3)
flutter: ════════════════════════════════════════════════════════════════════════════════════════════════════
flutter: Another exception was thrown: NoSuchMethodError: The method '>' was called on null.

flutter: Another exception was thrown: NoSuchMethodError: The method '>' was called on null.

flutter: Another exception was thrown: NoSuchMethodError: The method '>' was called on null.

flutter: Another exception was thrown: NoSuchMethodError: The method '>' was called on null.
`