better mpeg2 TS elementary stream Access Unit parsing

mpeg2 es stream access units have a 3 byte prefix and a 1 byte start
code. Searching for the next access unit started after the prefix
instead of after the start byte.

Bug: 74114680
Test: ran POC before/after
(cherry picked from commit 371066d073c5db289b0f38b9d2bfd3e326c78c66)

Change-Id: I3c51c62355c810e1b8dbc644cad3de335b7d8108
1 file changed