Proposed fix for issue where closeConnectionIfNeeded() was initiating a _markNeedsBuild() during dispose, causing exception

[woodyhayday]

Proposed fix for issue where closeConnectionIfNeeded() was initiating a _markNeedsBuild() during dispose, causing exception

Using flutter_quill 11.4.1 I was hitting this error in my flutter app, where by:

1. Load a widget with Quill (whole screen editor, with back button)
2. User hits back button.
3. App copies text out of Quill.
4. App changes page (setPageIndex), which disposes the Quill widget.
5. Quill's dispose() fires closeConnectionIfNeeded()
6. Which changes RawEditorStateTextInputClientMixin._lastKnownRemoteTextEditingValue
7. Which notifies QuillRawEditorState._onComposingRangeChanged()
8. Which fires _markNeedsBuild() because mounted = true still

I'm an experienced engineer outside of dart, but I've been dabbling here for a few months. This may be the way my own app is setup, bungling the process, but I dug through this for a few hours and this PR was my best attempt at a fix today.

Here's the error stack:

PR Description

Reorders dispose() actions, making sure composingRange.removeListener(_onComposingRangeChanged); fires before closeConnectionIfNeeded() to avoid the latter firing the former and leading to an exception.

Type of Change

• 🛠️ Bug fix: Resolves an issue without changing current behavior.