avformat/argo_brp: remove block_align check for audio

avformat/argo_brp: remove block_align check for audio

Causes a divide-by-zero in the rare case where:
- the file has an audio stream,
- the first audio frame isn't within the first BRP_BASF_LOOKAHEAD frames,
- an audio frame is encountered later, and
- its chunk header (except num_blocks) contains all zeros
   (matching the uninitialised structure in the context)

The decoder will discard any garbage data, so the check isn't really needed.

Fixes: division by 0
Fixes: 26667/clusterfuzz-testcase-minimized-ffmpeg_dem_ARGO_BRP_fuzzer-5645146928185344.fuzz
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Zane van Iperen <zane@zanevaniperen.com>