mpegts: fix demuxing PES private stream 2

PES header size is 6 bytes (00 00 01 bf XX XX), not 0.
BluRay text subtitles use private stream 2.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mpegts.c

@@ -1054,6 +1054,7 @@ static int mpegts_push_data(MpegTSFilter *filter,
                             pes->st->request_probe = 1;
                         }
                     } else {
+                        pes->pes_header_size = 6;
                         pes->state      = MPEGTS_PAYLOAD;
                         pes->data_index = 0;
                     }