[NUI] fix layouter null exception while clearing it (#3156)

diff --git a/src/Tizen.NUI.Components/Controls/RecyclerView/Layouter/ItemsLayouter.cs b/src/Tizen.NUI.Components/Controls/RecyclerView/Layouter/ItemsLayouter.cs
index 1b4ff1e..00964cc 100755 (executable)
--- a/src/Tizen.NUI.Components/Controls/RecyclerView/Layouter/ItemsLayouter.cs
+++ b/src/Tizen.NUI.Components/Controls/RecyclerView/Layouter/ItemsLayouter.cs
@@ -149,11 +149,14 @@ namespace Tizen.NUI.Components
         /// <since_tizen> 9 </since_tizen>
         public virtual void Clear()
         {
-            foreach (RecyclerViewItem item in VisibleItems)
+            if (VisibleItems != null)
             {
-                if (ItemsView != null) ItemsView.UnrealizeItem(item, false);
+                foreach (RecyclerViewItem item in VisibleItems)
+                {
+                    if (ItemsView != null) ItemsView.UnrealizeItem(item, false);
+               }
+                VisibleItems.Clear();
             }
-            VisibleItems.Clear();
             if (CandidateMargin != null)
             {
                 CandidateMargin.Dispose();