[mythtv-cmyth] Demuxing MPEG-TS: Stream info setup

Add new member 'is_setup' to trace feed of stream info.
Value is updated to true on call SetVideoInformations and SetAudioInformations.
Also true for stream using default parser on new instance or does'nt require setup.
[mythtv-cmyth] Demuxer: Scratch killer

Wait until setup is completed before returning stream info.