Method EnableTextfileButton

src/help_gui.cpp:172–175

private:
	void EnableTextfileButton(std::string_view filename, Subdirectory subdir, WidgetID button_widget)
	{
		this->GetWidget<NWidgetLeaf>(button_widget)->SetDisabled(!FindGameManualFilePath(filename, subdir).has_value());
	}
};

static constexpr std::initializer_list<NWidgetPart> _nested_helpwin_widgets = {