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
Bug: 160265164
Test: tests/spdif_tests.cpp
Change-Id: Ifc7f8c8946388e19f39f35d649a5936568f8b9b2
Merged-In: Ifc7f8c8946388e19f39f35d649a5936568f8b9b2
(cherry picked from commit 1f73a728ef4b6d7d350c0715bdb10d59e5b5f9be)
4 files changed