Use pointer for decimal.Decimal
Use pointer for decimal.Decimal

Fix breakage caused by 54efccb61ffe0a31b6a1908bdc8a35f491da01ea in
https://github.com/shopspring/decimal

plopik/pgx,silviucm/pgx,plopik/pgx,jackc/pgx,jackc/pgx,plopik/pgx,silviucm/pgx,jackc/pgx,silviucm/pgx,jackc/pgx