This undoes a mistake in 1ec7679f: domainval and domainnull were
meant to live across loop iterations, but they were incorrectly
moved inside the loop.  The effect was only to emit useless extra
EEOP_MAKE_READONLY steps, so it's not a big deal; nonetheless,
back-patch to v13 where the mistake was introduced.

Ranier Vilela

Discussion: https://postgr.es/m/CAEudQAqXuhbkaAp-sGH6dR6Nsq7v28_0TPexHOm6FiDYqwQD-w@mail.gmail.com