[BUG] RxApp.SuspensionHost.GetAppState sometimes returns null due to concurrency issues

[tomasfil]

Describe the bug

Sometimes upon restoring AppState, the state would be null, because GetAppState can be called before app gets loaded and thus before suspension driver loaded app state.
https://user-images.githubusercontent.com/34779382/155291750-546fa71a-8897-4a30-9e8a-7205d1ace8a4.mp4

Expected behaviour

GetAppState should always return object, not null.

[github-actions]

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