pgsql: Harden PL/Perl code against "tied" Perl arrays and hashes.

Harden PL/Perl code against "tied" Perl arrays and hashes.

Tied arrays might report different sizes each time they are inspected.
To avoid generating a corrupt result array, fix plperl_array_to_datum()
to read av_len() of each input array only once. If the input does
appear to get shorter, we'll fill nulls for the now-missing entries,
which seems fine. Conversely, if it gets longer, we'll ignore the new
entries.

plperl_to_hstore() assumed that Perl's hv_iterinit() returns the
number of entries in the given Perl hash. Usually that's true,
but per the Perl docs, "the return value is currently only meaningful
for hashes without tie magic". That could potentially end in a memory
stomp. We don't depend on that result value anywhere else, so don't
do so here either.

Reported-by: Hcamael <baiyjrh(at)gmail(dot)com>
Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Reviewed-by: Andrew Dunstan <andrew(at)dunslane(dot)net>
Backpatch-through: 14
Security: CVE-2026-14670

Branch
------
REL_16_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/477a6bdb086106fb5b0bf5b87f01fffd8393d340
Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>

Modified Files
--------------
contrib/hstore_plperl/hstore_plperl.c | 11 +++++++++--
src/pl/plperl/plperl.c | 6 +++++-
2 files changed, 14 insertions(+), 3 deletions(-)