Two MPLS parsing issues:
1. PGS subtitle (0x90) appearing in audio stream slot: language was read
from audio offset sa[2..5] instead of PG offset sa[1..4], causing
truncation ("ng " instead of "eng"). Fixed by detecting PGS coding
type in audio slots and using correct offset.
2. Secondary PG (PiP subtitle) entries were not consumed, causing
position tracking to drift. Added missing n_pip_pg loop.
3. Added stream_type 5/6/7 attribute parsing for secondary audio/video.
MattJackson
7fcbcff6e5