Codechange: Close dropdowns by class instead of id.

src/widgets/dropdown.cpp

@@ -339,7 +339,7 @@ struct DropdownWindow : Window {
  */
 void ShowDropDownListAt(Window *w, DropDownList &&list, int selected, int button, Rect wi_rect, Colours wi_colour, bool instant_close)
 {
-	CloseWindowById(WC_DROPDOWN_MENU, 0);
+	CloseWindowByClass(WC_DROPDOWN_MENU);
 
 	/* The preferred position is just below the dropdown calling widget */
 	int top = w->top + wi_rect.bottom + 1;