[SuperEditor][Bug][iOS] - Error when initializing the composer with a non-null initial selection.

[matthew-carroll]

In a client app, when initializing the composer with a selection on iOS, we get the following error:

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
The following _TypeError was thrown building IosHandlesDocumentLayer(dirty, state:
IosControlsDocumentLayerState#6fb86):
Null check operator used on a null value

When the exception was thrown, this was the stack:
#0      IosControlsDocumentLayerState.computeLayoutDataWithDocumentLayout (package:super_editor/src/infrastructure/platforms/ios/ios_document_controls.dart:752:75)
#1      DocumentLayoutLayerState.computeLayoutData (package:super_editor/src/infrastructure/documents/document_layers.dart:50:12)
#2      ContentLayerState.build (package:super_editor/src/infrastructure/content_layers.dart:708:21)
#3      StatefulElement.build (package:flutter/src/widgets/framework.dart:5934:27)
#4      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:5820:15)
#5      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:5985:11)

[tranthequang]

Thanks for reporting this issue.

I may be able to prepare a focused PR for this, but I need a bit more implementation context first.

Could you please clarify:

1. Which file/module/page is affected?
2. Current behavior
3. Expected behavior
4. Reproduction steps/logs/screenshots if available

Once clarified, I can continue with a targeted fix.