pgsql: Improve comment for OAT_POST_CREATE.

Improve comment for OAT_POST_CREATE.

Clarify that the command counter may or may not have been incremented.

We may want to change the behavior to be more consistent, but until
that time, at least improve the comment.

Discussion: https://postgr.es/m/CAHoZxqvN2eoic_CvjsAvpryyLyA2xG8JmsyMtKFFJz_1oFhfOg%40mail.gmail.com
Reported-by: Mary Xu

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/bb44a6ba48edfe1ac8bca87b1f2cfdcd9f86c930

Modified Files
--------------
src/include/catalog/objectaccess.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)