Need to do CommandCounterIncrement after StoreAttrMissingVal.

Need to do CommandCounterIncrement after StoreAttrMissingVal.

Without this, an additional change to the same pg_attribute row
within the same command will fail.  This is possible at least with
ALTER TABLE ADD COLUMN on a multiple-inheritance-pathway structure.
(Another potential hazard is that immediately-following operations
might not see the missingval.)

Introduced by 95f650674, which split the former coding that
used a single pg_attribute update to change both atthasdef and
atthasmissing/attmissingval into two updates, but missed that
this should entail two CommandCounterIncrements as well.  Like
that fix, back-patch through v13.

Reported-by: Alexander Lakhin <[email protected]>
Author: Tender Wang <[email protected]>
Reviewed-by: Tom Lane <[email protected]>
Discussion: https://postgr.es/m/025a3ffa-5eff-4a88-97fb-8f583b015965@gmail.com
Backpatch-through: 13