Only apply Base.Sort.SubArrayOptimization when iszero(v.offset1) (#59572)
Fixes #59569
Thanks @N5N3 for finding the bug!
For 1.13, we could re-enable this optimization and propagate the
information to the sub-alg or have the sub-alg's embedded indices be
relative to `kw.lo` rather than absolute. For backports, this minimal
change is more appropriate.
(cherry picked from commit 067b0133a8ec3f5c81d89525cd6cb4f25df6cb9c)