Fix 8c58fb1efd: Doubled beep sounds when clicking toolbar buttons.

* ShowDropDownList() now issues a beep, so individual toolbar buttons no longer need to do it.
* HandleButtonClick() may be called twice for some buttons, as it is called by automatically for PUSH buttons.

This caused some beeps to sound louder than others.

src/window.cpp

@@ -603,6 +603,9 @@ EventState Window::OnHotkey(int hotkey)
  */
 void Window::HandleButtonClick(WidgetID widget)
 {
+	/* Button click for this widget may already have been handled. */
+	if (this->IsWidgetLowered(widget) && this->timeout_timer == TIMEOUT_DURATION) return;
+
 	this->LowerWidget(widget);
 	this->SetTimeout();
 	this->SetWidgetDirty(widget);