BUG #15833: defining a comment on a domain constraint fails with wrong OID

The following bug has been logged on the website:

Bug reference:      15833
Logged by:          Clemens Ladisch
Email address:      clemens@ladisch.de
PostgreSQL version: 10.8
Operating system:   Windows 64-bit
Description:

postgres=> CREATE DOMAIN ddd AS text CONSTRAINT ccc CHECK (TRUE);
CREATE DOMAIN
postgres=> COMMENT ON CONSTRAINT ccc ON DOMAIN ddd IS 'test';
ERROR:  42704: type with OID 444275 does not exist
LOCATION:  pg_type_ownercheck, aclchk.c:4585

And there is indeed no type with that OID:

postgres=> SELECT 'type', oid FROM pg_type WHERE typname = 'ddd' UNION ALL
SELECT 'constraint', oid FROM pg_constraint WHERE conname = 'ccc';
  ?column?  |  oid
------------+--------
 type       | 444274
 constraint | 444275
(2 rows)

Same with Postgres 9.6 on SQLFiddle:
<http://www.sqlfiddle.com/#!17/a63b6/2>