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ARROW-12077: [C++] Fix out-of-bounds write in ListArray::FromArrays

This fixes an out-of-bounds write that mimalloc caught during free(). ListArray::FromArrays does some sanitization, but had an off-by-N error: for a length N array, given N + 1 offsets, it correctly copied N validity bits from the offset array, but then tried to clear the N+2nd bit. Usually this would be fine anyways, given that there would be extra bits/bytes in validity buffer, but not always.

Closes #9801 from lidavidm/arrow-12077

Authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>