fixed a bug of CoverView

src/Shared/HandyControl_Shared/Controls/Cover/CoverView/CoverView.cs

@@ -223,7 +223,7 @@ namespace HandyControl.Controls
             {
                 ItemsHost.Children.Remove(_viewContent);
             }
-            var total = Items.Count + 1;
+            var total = _entryDic.Count + 1;
             var totalRow = total / Groups + (total % Groups > 0 ? 1 : 0);
             if (total <= Groups)
             {
@@ -359,9 +359,9 @@ namespace HandyControl.Controls
         private void GenerateIndex()
         {
             var index = 0;
-            foreach (var item in Items)
+            foreach (var item in _entryDic.Values)
             {
-                _entryDic[item].Index = index++;
+                item.Index = index++;
             }
         }