[NUI] Fix not to dereference nullable handle ItemsLayouter

ItemsLayouter is nullable handle so it is checked before it is
dereferenced.

diff --git a/src/Tizen.NUI.Components/Controls/RecyclerView/CollectionView.cs b/src/Tizen.NUI.Components/Controls/RecyclerView/CollectionView.cs
index 8703511..f5557df 100755 (executable)
--- a/src/Tizen.NUI.Components/Controls/RecyclerView/CollectionView.cs
+++ b/src/Tizen.NUI.Components/Controls/RecyclerView/CollectionView.cs
@@ -938,7 +938,7 @@ namespace Tizen.NUI.Components
         {
             // Destination is depending on implementation of layout manager.
             // Get destination from layout manager.
-            return ItemsLayouter.CalculateCandidateScrollPosition(position);
+            return ItemsLayouter?.CalculateCandidateScrollPosition(position) ?? position;
         }
 
         /// <summary>
@@ -951,7 +951,7 @@ namespace Tizen.NUI.Components
         {
             if (disposed) return;
 
-            if (needInitalizeLayouter)
+            if (needInitalizeLayouter && (ItemsLayouter != null))
             {
                 ItemsLayouter.Initialize(this);
                 needInitalizeLayouter = false;