Fix: Prevent crash when default layout preferences are applied to empty paths

[seer-by-sentry]

Resolved / Related Issues

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• Closes FILES-APP-4WS

Steps used to test these changes

Stability is a top priority for Files and all changes are required to go through testing before being merged into the repo. Please include a list of steps that you used to test this PR.

1. Reproduced the original issue by triggering the condition where an uninitialized WorkingDirectory is passed to GetLayoutPreferencesForPath during setting change events.
2. Verified that the path.StartsWith() method throws a NullReferenceException without the fix.
3. Applied the fix by adding checks to prevent applying default layout preferences when the path is null or empty.
4. Confirmed that the NullReferenceException is no longer thrown after applying the fix.
5. Tested with various scenarios involving empty paths and uninitialized WorkingDirectory to ensure the fix handles all cases.
6. Ensured that the application functions as expected and no unexpected behavior occurs when dealing with empty paths or uninitialized WorkingDirectory.

[hishitetsu]

I think simply checking for null should be sufficient.