avformat/mpegts: Continue parsing PMTs until at least 2 streams are found or 100kb are reached

This (ugly) hack fixes Ticket3348
If someone has an idea on how to fix this nicer, that would be very welcome
but the stream contains several PMTs with just one of the 2 streams at the start

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
