Fix Windows Snackbar Registration

[ne0rrmatrix]

Description of Change

Fixes a bug where you open and close multiple secondary windows in a Windows environment and have snackbar registered. This prevents the crash that occurs otherwise. This changes the check for Application.Current.Windows.Count from 1 to 0 in OnClosed method for builder Configuration lifecycle events.

Linked Issues

• Fixes [BUG] Crash on second window close when SnackBar enabled on Windows (still reproducible in v12.0.0) #2754

PR Checklist

• Has a linked Issue, and the Issue has been approved(bug) or Championed (feature/proposal)
• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Changes adhere to coding standard
• Documentation created or updated: https://github.com/MicrosoftDocs/CommunityToolkit/pulls

Additional information

There was a previous attempt to fix this but it set window count to unregister at 1 and not zero. After verifying that when app exits it does call LifeCycle events for OnClosed during shutdown when Application.Current is not null and windows count is zero I created this PR to address the issue.

[Copilot]

Pull Request Overview

This PR fixes a bug in the Windows snackbar registration logic by adjusting the check for the number of windows open during the application shutdown.

• Changed the condition from checking for 1 open window to checking for 0 open windows in the OnClosed method.
• Ensures that notifications are unregistered only when there are no open windows, preventing crashes during app shutdown.

Comments suppressed due to low confidence (1)

src/CommunityToolkit.Maui/Options.cs:90

• The condition has been correctly updated from a check against 1 to 0, which should ensure that snackbar notifications are unregistered only when no windows remain. Please verify that this logic aligns with the overall lifecycle management of window events during app shutdown.

						else if (Application.Current.Windows.Count is 0)

[bijington]

Thanks @ne0rrmatrix