修改添加位置

SpineViewer/src/SpineListView.cs

@@ -36,9 +36,9 @@ namespace SpineViewer
         /// </summary>
         private void Insert(int index = -1)
         {
-            // 如果索引无效则插在开头
+            // 如果索引无效则在末尾添加
             if (index < 0 || index > spines.Count)
-                index = 0;
+                index = spines.Count;
 
             var dialog = new OpenSpineDialog();
             if (dialog.ShowDialog() != DialogResult.OK)