make create_mac_string more robust
make create_mac_string more robust

simon-weber/Unofficial-Google-Music-API,peetahzee/Unofficial-Google-Music-API,nvbn/Unofficial-Google-Music-API,dvirtz/gmusicapi,dvirtz/gmusicapi,tanhaiwang/gmusicapi,jimyx17/gmusic,TheOpenDevProject/gmusicapi,simon-weber/gmusicapi,thebigmunch/gmusicapi