A grouped query over an empty MyISAM LEFT JOIN returns empty because an unused window AVG corrupts MAX()

the inner derived table is exactly `(NULL, 2)` and `(NULL, 9)`, so after `GROUP BY c1` the unique group's `MAX(c4)` must be `9`. MariaDB instead computes `MAX(c4)` as `2`, so the outer predicate `m = 9` wrongly filters the only row away.

CREATE TABLE t1(c1 INT) ENGINE=MyISAM;
CREATE TABLE t2(c0 INT UNIQUE);

INSERT INTO t2 VALUES (9), (2);

SELECT 1
FROM (
SELECT MAX(subq0.c4) AS m, AVG(subq0.c4) OVER () AS a
FROM (
SELECT t1.c1, t2.c0 AS c4
FROM t2
LEFT JOIN t1
ON (FALSE)
) AS subq0
GROUP BY subq0.c1
) AS q
WHERE m = 9; – Expected correct result: 1 – actual Wrong result: <empty>