plugins.twitch: Fix validation bug.
plugins.twitch: Fix validation bug.

streamlink/streamlink,back-to/streamlink,gtmanfred/livestreamer,streamlink/streamlink,wlerin/streamlink,beardypig/streamlink,Feverqwe/livestreamer,hmit/livestreamer,jtsymon/livestreamer,lyhiving/livestreamer,chhe/livestreamer,flijloku/livestreamer,sbstp/streamlink,caorong/livestreamer,beardypig/streamlink,chrippa/livestreamer,lyhiving/livestreamer,programming086/livestreamer,mmetak/streamlink,flijloku/livestreamer,Feverqwe/livestreamer,melmorabity/streamlink,okaywit/livestreamer,hmit/livestreamer,programming086/livestreamer,melmorabity/streamlink,ethanhlc/streamlink,intact/livestreamer,wolftankk/livestreamer,blxd/livestreamer,derrod/livestreamer,chhe/streamlink,gravyboat/streamlink,wolftankk/livestreamer,charmander/livestreamer,chhe/streamlink,fishscene/streamlink,chhe/livestreamer,gravyboat/streamlink,ethanhlc/streamlink,Dobatymo/livestreamer,back-to/streamlink,bastimeyer/streamlink,Klaudit/livestreamer,Dobatymo/livestreamer,fishscene/streamlink,Saturn/livestreamer,chrippa/livestreamer,derrod/livestreamer,gtmanfred/livestreamer,javiercantero/streamlink,charmander/livestreamer,bastimeyer/streamlink,wlerin/streamlink,Klaudit/livestreamer,okaywit/livestreamer,intact/livestreamer,Masaz-/livestreamer,sbstp/streamlink,Saturn/livestreamer,caorong/livestreamer,mmetak/streamlink,javiercantero/streamlink,blxd/livestreamer,Masaz-/livestreamer,jtsymon/livestreamer