Fix - Complete window dialog task when dialog is hidden

[emmauss]

What does the pull request do?

When a dialog window is hidden, sets the task returned with ShowDialog as complete.

What is the current behavior?

When a dialog window is shown, a task is return for user to wait on. This task is set to completed on Close, but not on Hide, even though the owner is set to null when hidden. This makes any thread waiting on the window to lock up.

What is the updated/expected behavior with this PR?

How was the solution implemented (if it's not obvious)?

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

Obsoletions / Deprecations

Fixed issues

[avaloniaui-bot]

You can test this PR using the following package version. 11.3.999-cibuild0054544-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[kekekeks]

Don't we also need to update "this window has child modal dialogs" state for dialog parent?

[kekekeks]

Nvm, Owner is already set to null in Hide.