Re: use-after-free in jsonb_set_lax()

Hi John,

> Please don't copy and paste LLM output into emails.

It wasn't pasted; it's a real build here. The repro and the ASan report
(with my build paths in it) are attached. It runs under an ASan build in
a couple of seconds.

The point, short: on a non-assert build this is not only a crash. The
ASan report (attached) is heap-use-after-free, READ of size 1 at a
freed address, in jsonb_set at jsonfuncs.c:4859 reached from
jsonb_set_lax at 4917. The freed read lands in the value jsonb_set
returns, so the result can carry reused heap, not just wrong data. That
is what seemed worth a line for the back-branches. v1 is clean over the
multi-row cases I ran.

Regards,
Manu