This fixes assert failures, when a (corrupt/fuzzed) bitstream
doesn't trigger starting/ending CRCs properly (or when decoding
is aborted halfway when an error is encountered). Skipping ending
a CRC region doesn't trigger an assert failure, but when a later
CRC region is started and ended, an assert fails when the end
doesn't match the expected CRC region.
Fixes: 1928/clusterfuzz-testcase-minimized-6480505958563840
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg