spdif: fix possible buffer overflow

SPDIF burst buffer could overflow if given bad data.
Check for frmsiz in header being too low.
Prevent numeric overflow in pending bytes calculation.
Prevent numeric overflow when checking for buffer overflow.

Bug: 145262423
Test: tests/spdif_tests.cpp
Change-Id: Ifc7f8c8946388e19f39f35d649a5936568f8b9b2
Merged-In: Ifc7f8c8946388e19f39f35d649a5936568f8b9b2
4 files changed