pgsql: Fix bogus CALLED_AS_TRIGGER() defenses.

Fix bogus CALLED_AS_TRIGGER() defenses.

contrib/lo's lo_manage() thought it could use
trigdata->tg_trigger->tgname in its error message about
not being called as a trigger. That naturally led to a core dump.

unique_key_recheck() figured it could Assert that fcinfo->context
is a TriggerData node in advance of having checked that it's
being called as a trigger. That's harmless in production builds,
and perhaps not that easy to reach in any case, but it's logically
wrong.

The first of these per bug #16340 from William Crowell;
the second from manual inspection of other CALLED_AS_TRIGGER
call sites.

Back-patch the lo.c change to all supported branches, the
other to v10 where the thinko crept in.

Discussion: https://postgr.es/m/16340-591c7449dc7c8c47@postgresql.org

Branch
------
REL_12_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/d56657c35d9cd442438754c68b9aaa30e6720cc4

Modified Files
--------------
contrib/lo/lo.c | 3 +--
src/backend/commands/constraint.c | 2 +-
2 files changed, 2 insertions(+), 3 deletions(-)