Fix wrong error message from pg_get_tablespace_ddl() - Mailing list pgsql-hackers

Hi,

I started testing pg_get_tablespace_ddl(). While tracing pg_get_tablespace_ddl_internal(), I noticed that this error
reportmust be wrong: 
```
    /* User must have SELECT privilege on pg_tablespace. */
    if (pg_class_aclcheck(TableSpaceRelationId, GetUserId(), ACL_SELECT) != ACLCHECK_OK)
    {
        ReleaseSysCache(tuple);
        aclcheck_error(ACLCHECK_NO_PRIV, OBJECT_TABLESPACE, spcname);
    }
```

The comment clearly says that SELECT privilege on pg_tablespace is required, but the error is reported against the
targettablespace instead. 

This is easy to reproduce:
```
evantest=# set allow_in_place_tablespaces = true;
SET
evantest=# create role r1;
CREATE ROLE
evantest=# create tablespace ts1 location '';
CREATE TABLESPACE
evantest=# revoke select on pg_tablespace from r1;
REVOKE
evantest=# set role r1;
SET
evantest=> select * from pg_get_tablespace_ddl('ts1');
ERROR:  permission denied for tablespace ts1
```

Attached is a simple one-line fix. Attached is a simple one-line fix. I did not add a new test, as we usually try to
avoidextending the test time for such a small fix. With the fix, the error message now looks like: 
```
evantest=> select * from pg_get_tablespace_ddl('ts1');
ERROR:  permission denied for table pg_tablespace
```

Oops, I was one of the reviewers of the original patch. Sorry for not finding this during review.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/