Duplicate subqueries produce incorrect results #21210

  CREATE TABLE t1(id INTEGER) AS VALUES (1), (2), (3);
  CREATE TABLE t2(id INTEGER, outer_id INTEGER) AS VALUES (10, 1), (20, 1), (30, 2);

  SELECT
    (SELECT count(*) AS c FROM t2 WHERE t2.outer_id = t1.id) + 1 AS a,
    (SELECT count(*) AS c FROM t2 WHERE t2.outer_id = t1.id) + 2 AS b
  FROM t1
  ORDER BY t1.id;

  +---+---+
  | a | b |
  +---+---+
  | 3 | 4 |
  | 2 | 3 |
  | 1 | 2 |
  +---+---+

  +------+---+
  | a    | b |
  +------+---+
  | 3    | 4 |
  | 2    | 3 |
  | NULL | 2 |
  +------+---+