优化 PinCode 类

如果粘贴内容有效，则执行 `CompleteCommand` 并触发 `CompleteEvent` 事件。

src/Ursa/Controls/PinCode/PinCode.cs

@@ -181,6 +181,11 @@ public class PinCode: TemplatedControl
                         presenter.Text = newText[i].ToString();
                     }
                 }
+                if (newText.Length == Count)
+                {
+                    CompleteCommand?.Execute(Digits);
+                    RaiseEvent(new PinCodeCompleteEventArgs(Digits, CompleteEvent));
+                }
             }
             return;
         }