Allow post_show to override a window's retval

src/gui/dialogs/dialog.cpp

@@ -68,6 +68,9 @@ bool tdialog::show(CVideo& video, const unsigned auto_close_time)
 
 	post_show(*window);
 
+	// post_show may have updated the windoe retval. Update it here.
+	retval_ = window->get_retval();
+
 	return retval_ == twindow::OK;
 }
 

src/gui/widgets/window.hpp

@@ -425,6 +425,11 @@ public:
 			close();
 	}
 
+	int get_retval()
+	{
+		return retval_;
+	}
+
 	void set_owner(tdialog* owner)
 	{
 		owner_ = owner;