Revert "Fix exception when adding a new Rule when no Rule is selected (#278)"

This reverts commit ae01f64.

Author: ChuanXin-Unity

Editor/Tiles/RuleTile/RuleTileEditor.cs

@@ -274,8 +274,7 @@ private void OnAddElement(object obj)
             else
             {
                 tile.m_TilingRules.Insert(list.index + 1, rule);
-                if (list.IsSelected(list.index))
-                    list.index += 1;
+                list.index += 1;
             }
         }
 
@@ -288,13 +287,12 @@ private void OnDuplicateElement(object obj)
             var copyRule = tile.m_TilingRules[list.index];
             var rule = copyRule.Clone();
             tile.m_TilingRules.Insert(list.index + 1, rule);
-            if (list.IsSelected(list.index))
-                list.index += 1;
+            list.index += 1;
         }
 
         private void OnAddDropdownElement(Rect rect, ReorderableList list)
         {
-            if (0 <= list.index && list.index < tile.m_TilingRules.Count && list.IsSelected(list.index))
+            if (0 <= list.index && list.index < tile.m_TilingRules.Count)
             {
                 GenericMenu menu = new GenericMenu();
                 menu.AddItem(EditorGUIUtility.TrTextContent("Add"), false, OnAddElement, list);