🐛 Scrollbar's hover animation controller error

[harlanx]

Describe the bug
Animation controller.reverse() is called even when the Scrollbar Widget is removed from the tree which produces the error below.

[ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: 'package:flutter/src/animation/animation_controller.dart': Failed assertion: line 487 pos 7: '_ticker != null': AnimationController.reverse() called after AnimationController.dispose()
AnimationController methods should not be used after calling dispose.
#0      _AssertionError._doThrowNew (dart:core-patch/errors_patch.dart:51:61)
#1      _AssertionError._throwNew (dart:core-patch/errors_patch.dart:40:5)
#2      AnimationController.reverse (package:flutter/src/animation/animation_controller.dart:487:7)
#3      _ScrollbarState.handleHover (package:fluent_ui/src/controls/utils/scrollbar.dart:167:30)
<asynchronous suspension>

To Reproduce
Steps to reproduce the behavior:

1. Create a conditional widget that removes Scrollbar and it's descendants from widget tree.
2. Hover on scrollbar
3. Trigger condition to remove Scrollbar widget from tree.
4. See error

Additional context
It only produces the error if the scrollbar is hovered.