pgsql: Avoid low-probability crash on out-of-memory.

Avoid low-probability crash on out-of-memory.

check_restrict_nonsystem_relation_kind() correctly uses guc_malloc()
in v16 and later.  But in older branches it must use malloc()
directly, and it forgot to check for failure return.
Faulty backpatching of 66e94448a.

Karina Litskevich

Discussion: https://postgr.es/m/CACiT8iZ=atkguKVbpN4HmJFMb4+T9yEowF5JuPZG8W+kkZ9L6w@mail.gmail.com

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/cd1c8b992e9f8774f9e08b2c7f668067bfe7e621

Modified Files
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src/backend/tcop/postgres.c | 5 +++++
1 file changed, 5 insertions(+)