vp9: fix OOB read in decoder_peek_si_internal

Profile 1 or 3 bitstreams may require 11 bytes for the header in the
intra-only case.

Additionally add a check on the bit reader's error handler callback to
ensure it's non-NULL before calling to avoid future regressions.

This has existed since at least (pre-1.4.0):
09bf1d61c Changes hdr for profiles > 1 for intraonly frames

BUG=webm:1543,867792

Change-Id: I23901e6e3a219170e8ea9efecc42af0be2e5c378
(cherry picked from commit 0681cff1ad36b3ef8ec242f59b5a6c4234ccfb88)
3 files changed