svtplay: dont crash when it cant find any streams
svtplay: dont crash when it cant find any streams

In some cases we cant download any videos. when they are only
provided for flash users and not iOS users.

leakim/svtplay-dl,OakNinja/svtplay-dl,qnorsten/svtplay-dl,dalgr/svtplay-dl,dalgr/svtplay-dl,selepo/svtplay-dl,qnorsten/svtplay-dl,leakim/svtplay-dl,OakNinja/svtplay-dl,selepo/svtplay-dl,olof/svtplay-dl,spaam/svtplay-dl,OakNinja/svtplay-dl,olof/svtplay-dl,iwconfig/svtplay-dl,iwconfig/svtplay-dl,spaam/svtplay-dl,leakim/svtplay-dl