Method SetSelectedClass

src/rail_gui.cpp:1818–1818

	void Close(int) override { ResetObjectToPlace(); }
	int GetSelectedClass() const override { return _waypoint_gui.sel_class; }
	void SetSelectedClass(int id) const override { _waypoint_gui.sel_class = this->GetClassIndex(id); }

	StringID GetClassName(int id) const override
	{