Fix null reference when window is null

When using certain controls ie bottom sheets and search bars there can be a crash when the keyboard displays. Check for null & return early if it is.

src/Core/src/Platform/iOS/KeyboardAutoManagerScroll.cs

@@ -1,4 +1,4 @@
-/*
+/*
  * This class is adapted from IQKeyboardManager which is an open-source
  * library implemented for iOS to handle Keyboard interactions with
  * UITextFields/UITextViews. Link to their MIT License can be found here:
@@ -311,6 +311,11 @@ internal static void AdjustPosition()
 		var rootViewOrigin = new CGPoint(ContainerView.Frame.GetMinX(), ContainerView.Frame.GetMinY());
 		var window = ContainerView.Window;
 
+		if (window is null)
+		{
+			return;
+		}
+
 		var intersectRect = CGRect.Intersect(KeyboardFrame, window.Frame);
 		var kbSize = intersectRect == CGRect.Empty ? new CGSize(KeyboardFrame.Width, 0) : intersectRect.Size;