[BUG] Setting custom ViewContractObservable on RoutedViewHost is not working

[deryaza]

Describe the bug

Setting custom ViewContractObservable on RoutedViewHost is not passing contract to the view resolver

Steps To Reproduce

RoutedViewHost.ViewContractObservable = Observable.Return("contract");
RoutedViewHost.Router.Navigate.Execute(vmWithViewWithContract);

Environment

• OS: windows
• Device: wpf, windows
• ReactiveUI Version: cloned from commit 8628353

Additional context

ReactiveUI/src/ReactiveUI.Uwp/Common/RoutedViewHost.cs

Line 106 in 8628353

this.WhenAnyObservable(x => x.ViewContractObservable).Do(x => _viewContract = x).StartWith(ViewContract),

removing StartWith in this line resolves it (not sure why tho).