[bug] relcache leaks in get_object_address

I noticed a problem of get_object_address() with missing_ok = true.

When we try to solve the name of nonexistent rule/trigger/constraint on
a particular existing table, get_object_address_relobject() opens the
relation, but address.objectId = InvalidOid shall be set.

I think it should be closed if the queried object was missing, although
existing code does not invoke get_object_address() with missing_ok = true.

Thanks,
-- 
KaiGai Kohei <kaigai@kaigai.gr.jp>