fix issue

LottoPicker/LottoPicker/Dialog/HistoryDialog.cs

@@ -67,6 +67,7 @@ namespace LottoPicker.Dialog
 
         private void PrintHistory(Dictionary<string, int> history)
         {
+            txtResult.Clear();
             StringBuilder stringBuilder = new StringBuilder();
             foreach (KeyValuePair<string, int> pair in history)
             {