Fix units mismatch in picture metadata limit checks#912
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FLAC__bitreader_limit_remaining() returns bits, but the picture metadata parser was comparing it directly against byte lengths for MIME type, description, and picture data fields. This meant fields with lengths between (limit/8, limit] could bypass the check. The actual read would still be caught by the downstream FLAC__bitreader_read_byte_block_aligned_no_crc which correctly converts bytes to bits before comparing, so this is not exploitable, but it is a correctness bug.
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FLAC__bitreader_limit_remaining() returns bits, but the picture
metadata parser was comparing it directly against byte lengths for
MIME type, description, and picture data fields. This meant fields
with lengths between (limit/8, limit] could bypass the check.
The actual read would still be caught by the downstream
FLAC__bitreader_read_byte_block_aligned_no_crc which correctly
converts bytes to bits before comparing, so this is not exploitable,
but it is a correctness bug.