Fixing view discovery for Unity for UWP

Fixing a bug when a page could not inherit its destination viewmodel because VML assumed that if we naviagte to page, then the page has to have a frame.

Source/Windows10/Prism.Unity.Windows/UnityContainerExtension.cs

@@ -49,7 +49,7 @@ public object Resolve(Type type, string name)
 
         public object ResolveViewModelForView(object view, Type viewModelType)
         {
-            if (view is Page page)
+            if (view is Page page && page.Frame != null)
             {
                 var service = NavigationService.Instances[page.Frame];
                 ResolverOverride[] overrides = null;