Improvements after live (#2013)

Author: kubaflo

src/Controls/src/Core/NavigationProxy.cs

@@ -212,7 +212,8 @@ protected virtual Task OnPushAsync(Page page, bool animated)
 			INavigation currentInner = Inner;
 			if (currentInner is null)
 			{
-				throw new InvalidOperationException("Page must be wrapped into a navigation page to perform navigation");
+				_pushStack.Value.Add(page);
+				return Task.FromResult(page);
 			}
 			return currentInner.PushAsync(page, animated);
 		}

src/Controls/src/Core/Window/Window.cs

@@ -679,6 +679,11 @@ public NavigationImpl(Window owner)
 				_owner = owner;
 			}
 
+			protected override Task OnPushAsync(Page page, bool animated)
+			{
+				throw new InvalidOperationException("Page must be wrapped into a navigation page to perform navigation");
+			}
+
 			protected override IReadOnlyList<Page> GetModalStack()
 			{
 				return _owner.ModalNavigationManager.ModalStack;