Codechange: Add enum items for dynmically created setting dropdowns.

src/widgets/script_widget.h

@@ -29,6 +29,8 @@ enum ScriptSettingsWidgets {
 	WID_SCRS_SCROLLBAR,  ///< Scrollbar to scroll through all settings.
 	WID_SCRS_ACCEPT,     ///< Accept button.
 	WID_SCRS_RESET,      ///< Reset button.
+
+	WID_SCRS_SETTING_DROPDOWN = -1, ///< Dynamically created dropdown for changing setting value.
 };
 
 /** Widgets of the #ScriptDebugWindow class. */