[UWP] Navigation breaks when back button is pressed

[pohzhiee]

Steps to reproduce:

1. Create a master-detail page with NavigationPage as the detail page
2. Navigate the from the detail page
3. Press back
4. Now left with previous detail page

[pohzhiee]

one way to fix is to do DependencyService for custom platform specific navigation implementation
https://docs.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/dependency-service/introduction