Fix: Fixed issue where HorizontalMultitaskingControl could have negative margin

[cinqmilleans]

Resolved / Related Issues
It happened to me that the appWindowTitleBar.RightInset value was negative. This value is provided by the sdk, we do not calculate it. This may cause an exception because GridLength does not accept a negative value. This pr fixes that problem.

Validation
How did you test these changes?

• Built and ran the app
• Tested the changes for accessibility

[yaira2]

How was it negative?

[cinqmilleans]

The HorizontalMultitaskingControl constructor throws an exception. This has no important consequence because it is intercepted by the xaml. However, there are 3 problems.

1. This exception is resource intensive.
2. If a future commit adds code to the end of this constructor, it cannot be executed randomly.
3. This may interfere with debugging another feature. The code should not cause any easily avoidable exceptions.

[yaira2]

How can I reproduce this issue?

[cinqmilleans]

I don't know how to reproduce it, but it's happened to me before.

[lukeblevins]

Should the system-provided inset values ever be negative? Obviously, if that's a possibility at this point, we'd want to prevent it.

Has a bug report for this been opened in microsoft/WindowsAppSDK?

[yaira2]

LGTM