properly. Otherwise the minimum of 1 is used and you can
only insert a single partition/slice and only at sector
0 (index 1).
o When adding a partition/slice, recalculate the index after
the start and size of the partition/slice are adjusted to
make them a multiple of the track size. Since the precheck
method sets the index based on the start of the partition
as provided by the user, we know that we're off by at most
1 and adjusting the index is safe.
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