return boost::none for key_code::vk_none in get_usage_page,get_usage
return boost::none for key_code::vk_none in get_usage_page,get_usage

jrolfs/Karabiner-Elements,tekezo/Karabiner-Elements,jrolfs/Karabiner-Elements,tekezo/Karabiner-Elements,jrolfs/Karabiner-Elements,jrolfs/Karabiner-Elements,tekezo/Karabiner-Elements,tekezo/Karabiner-Elements