pgsql: Mark multirange_constructor0() and multirange_constructor2() str

Mark multirange_constructor0() and multirange_constructor2() strict

These functions shouldn't receive null arguments: multirange_constructor0()
doesn't have any arguments while multirange_constructor2() has a single array
argument, which is never null.

But mark them strict anyway for the sake of uniformity.

Also, make checks for null arguments use elog() instead of ereport() as these
errors should normally be never thrown.  And adjust corresponding comments.

Catversion is bumped.

Reported-by: Peter Eisentraut
Discussion: https://postgr.es/m/0f783a96-8d67-9e71-996b-f34a7352eeef%40enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6bbcff096f932a1fe43ac3208c5c8b0acac29cda

Modified Files
--------------
src/backend/commands/typecmds.c         |  4 ++--
src/backend/utils/adt/multirangetypes.c | 25 +++++++++++++------------
src/include/catalog/catversion.h        |  2 +-
src/include/catalog/pg_proc.dat         | 24 ++++++++++++------------
4 files changed, 28 insertions(+), 27 deletions(-)