In #36 some of the odd errors were due to seeks beyond the end of the
disc. This was because the disc was "specially crafted" to be 25GB + 1
byte, which doesn't fit into the normal 512 byte sectors expected of a
disc. This lead to reads going beyond the end of the disc etc.
If a similarly evil disc is used with `losetup`, it just ignores the
last bytes of the disc that don't fit into 512 chunks. This is what
that patch does, logging an error at the same time.
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