Make pgss_post_parse_analyze() more consistent with the other hooks,
and avoid unnecessary overhead when pg_stat_statements.track=none.

Author: Raymond Martin
Reviewed-by: Fabien COELHO
Discussion: https://postgr.es/m/BN8PR21MB1217B003C4F79DE230AA36B9B1580%40BN8PR21MB1217.namprd21.prod.outlook.com