[desktop_multi_window v0.2.0] Invalid memory access upon app close

[isaacy13]

Upon closing app, there are various fatal memory access errors

Reproduce Steps

Steps to reproduce the behavior:

1. Open an app with desktop_multi_window v0.2.0
2. Close the app
3. See crash logs (e.g.: Sentry Native or debug locally with Visual Studio)

Expected behavior

Upon closing app, no memory access violations should occur

Version (please complete the following information):

• Flutter Version: v3.19.3
• OS: Windows
• plugin: [desktop_multi_window v0.2.0]

Errors occur in C++ library and are not caught by Flutter

Can debug locally with Visual Studio by:
- Open Task Manager
- Right click app
- Debug
- New instance of Visual Studio

Seems like desktop_multi_window objects are trying to be used after Flutter app is closed & memory is deallocated

Challenge might be making sure all objects are destructed before Flutter app is closed

Commenting out WindowChannel destructor code seems to resolve memory access errors, but was hoping for a better solution

Note: repro steps only require main window to be created (and registered) -- no creation of subwindows required to reproduce issue

[isaacy13]

Crash log dumps
0a27306d99e04b12ab0dc12b2e052135-symbolicated.txt
598f75b601014f48bd7a8f52d1ca6bc6-symbolicated.txt
51bef4fe07e04eb795279e3a6c32e8fc-symbolicated.txt
a9343bc9a4a840cba5d26cea13bda751-symbolicated.txt
b344426997b44e809894e49c6545b62f-symbolicated.txt