ReadNeedleBodyBytes sliced the needle body with the size from the needle
header without checking it. A corrupted .dat header carrying size -1 still
gets a positive body length (16 bytes on v3), so vacuum compaction read
that body and panicked with "slice bounds out of range [:-1]".
Writers never put a negative size in a .dat header: a delete appends a
size-0 record, and TombstoneFileSize only lives in the .idx. Reject a size
that is negative or leaves no room for the checksum/timestamp tail with an
error wrapping ErrorCorrupted. ScanVolumeFileFrom already logs body read
errors and moves on, so compaction now skips the record like any other
corrupt needle.
Fixes#6763
hsdfatandGitHub
5769057af3