JSON_MERGE_PATCH triggers a crash in mariadb

Hi,

The following test case triggers a crash in MariaDB.

SET @depth= 4000;

SET @j= CONCAT(REPEAT('{"a":', @depth), '0', REPEAT('}', @depth));

SELECT LEFT(JSON_MERGE_PATCH('{}', @j), 20) AS crash_probe;

I can reproduce this with the commit version f6e44c1b7819f9befa3824f07866822288231528 of MariaDB server in github repo.