Fix crash when selecting the selected item from a dropdown menu

src/gui/dialogs/drop_down_list.cpp

@@ -33,6 +33,14 @@ REGISTER_DIALOG(drop_down_list)
 namespace {
 	void click_callback(twindow& window, bool&, bool&, tpoint coordinate)
 	{
+		// By deselecting any selected row here, we remove the possibility that the click actually deselects the row
+		// and results in selected_item_ being set to -1.
+		// It works because this handler is called *before* the listbox's click handler.
+		tlistbox& list = find_widget<tlistbox>(&window, "list", true);
+		int sel = list.get_selected_row();
+		if(sel >= 0) {
+			list.select_row(sel, false);
+		}
 		SDL_Rect rect = window.get_rectangle();
 		if(coordinate.x < rect.x || coordinate.x > rect.x + rect.w || coordinate.y < rect.y || coordinate.y > rect.y + rect.h ) {
 			window.set_retval(twindow::CANCEL);