make all internal event handlers unignorable

source/gui/widgets/combox.cpp

@@ -240,7 +240,7 @@ namespace nana
 						//The lister window closes by itself. I just take care about the destroy event.
 						//The event should be destroy rather than unload. Because the unload event is invoked while
 						//the lister is not closed, if popuping a message box, the lister will cover the message box.
-						state_.lister->events().destroy.connect([this]
+						state_.lister->events().destroy.connect_unignorable([this]
 						{
 							_m_lister_close_sig();
 						});