pp_sort.c: fix fencepost error in call to av_extend()

In [rt.cpan.org #39196] issue #17496 there is a report
that Tie::File produced spurious blank lines in the file
after

    @tied= sort @tied;

it turns out that this is because Tie::File treats
EXTEND similarly to STORESIZE (which is arguably not
entirely correct, but also not that weird) coupled
with an off by one error in the calls to av_extend()
in pp_sort.

This patch fixes the fencepost error, adds some comments
to av_extend() to make it clear what it is doing, and
adds a test that EXTEND is called by this code with
correct argument.

0 files changed, 0 insertions, 0 deletions