SELECT ~0 on DOUBLE column: correct on MyISAM, wrong on InnoDB (signed LLONG_MAX)

Summary

On MariaDB 12.3.1-MariaDB-asan-log (rev 21a0714a), SELECT COUNT, ~0 on a DOUBLE column returns 18446744073709551615 on MyISAM (correct), but 9223372036854775807 on InnoDB (wrong). Integer columns behave correctly on both engines. This is a sibling of MDEV-39131: MyISAM is fixed, but InnoDB DOUBLE still triggers the old bug.

Minimal Reproducer

CREATE TABLE t_myisam (c0 DOUBLE) ENGINE = MyISAM;

INSERT INTO t_myisam VALUES (1);

SELECT COUNT(*), ~0 FROM t_myisam;

-- → 1, 18446744073709551615  (correct)

CREATE TABLE t_innodb (c0 DOUBLE) ENGINE = InnoDB;

INSERT INTO t_innodb VALUES (1);

SELECT COUNT(*), ~0 FROM t_innodb;

-- → 1, 9223372036854775807  (wrong)

Expected vs Actual

Notes

• Official MDEV-39131 fixed MyISAM; this report documents the InnoDB DOUBLE path that remains broken.
• Partial fix moved the bug to the former control engine.
• Issue is related to `Item_copy_string::val_int()` unsigned handling.

Environment

Suggested Fix

Apply MDEV-39131 unsigned handling for ~0 consistently for InnoDB DOUBLE result metadata paths, not only MyISAM.