fix: late initialization error

[LucasXu0]

I/flutter (11040): LateInitializationError: Local 'result' has not been initialized.
I/flutter (11040): #0      LateError._throwLocalNotInitialized (dart:_internal-patch/internal_patch.dart:189)
I/flutter (11040): #1      RenderObject.debugNeedsLayout (package:flutter/src/rendering/object.dart:2183)
I/flutter (11040): #2      _AppFlowyRichTextState.getCursorRectInPosition (package:appflowy_editor/src/editor/block_component/rich_text/appflowy_rich_text.dart:154)
I/flutter (11040): #3      DefaultSelectableMixin.getCursorRectInPosition (package:appflowy_editor/src/editor/block_component/rich_text/default_selectable_mixin.dart:48)
I/flutter (11040): #4      KeyboardServiceWidgetState._updateCaretPosition (package:appflowy_editor/src/editor/editor_component/service/keyboard_service_widget.dart:333)
I/flutter (11040): #5      KeyboardServiceWidgetState._onSelectionChanged (package:appflowy_editor/src/editor/editor_component/service/keyboard_service_widget.dart:218)
I/flutter (11040): #6      ChangeNotifier.notifyListeners (package:flutter/src/foundation/change_notifier.dart:433)
I/flutter (11040): #7      PropertyValueNotifier.value= (package:appflowy_editor/src/editor/util/property_notifier.dart:25)
I/flutter (11040): #8      EditorState.selection= (package:appflowy_editor/src/editor_state.dart:115)
I/flutter (11040): #9      EditorState.updateSelectionWithReason (package:appflowy_editor/src/editor_state.dart:224)
I/flutter (11040): #10     _MobileSelectionServiceWidgetState._onTapUp (package:appflowy_editor/src/editor/editor_component/service/selection/mobile_selection_service.dart:405)
I/flutter (11040): #11     MobileSelectionGestureDetectorState._tapDownDelegate (package:appflowy_editor/src/service/selection/mobile_selection_gesture.dart:119)
I/flutter (11040): #12     TapGestureRecognizer.handleTapUp.<anonymous closure> (package:flutter/src/gestures/tap.dart:649)
I/flutter (11040): #13     GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:315)
I/flutter (11040): #14     TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:649)
I/flutter (11040): #15     BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:309)
I/flutter (11040): #16     BaseTapGestureRecognizer.acceptGesture (package:flutter/src/gestures/tap.dart:279)
I/flutter (11040): #17     GestureArenaManager.sweep (package:flutter/src/gestures/arena.dart:167)
I/flutter (11040): #18     GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:499)
I/flutter (11040): #19     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:475)
I/flutter (11040): #20     RendererBinding.dispatchEvent (package:flutter/src/rendering/binding.dart:430)
I/flutter (11040): #21     GestureBinding._handlePointerEventImmediately (package:flutter/src/gestures/binding.dart:420)
I/flutter (11040): #22     GestureBinding.handlePointerEvent (package:flutter/src/gestures/binding.dart:383)
I/flutter (11040): #23     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:330)
I/flutter (11040): #24     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:299)
I/flutter (11040): #25     _invoke1 (dart:ui/hooks.dart:328)
I/flutter (11040): #26     PlatformDispatcher._dispatchPointerDataPacket (dart:ui/platform_dispatcher.dart:429)
I/flutter (11040): #27     _dispatchPointerDataPacket (dart:ui/hooks.dart:262)
3
I/flutter (11040): Another exception was thrown: Instance of 'DiagnosticsProperty<void>'