Bug #121216 VARCHAR column vs DATE constant: failed conversion silently acts as a "smallest sentinel"

Description:
mysql> -- Constant context (strict mode — correctly errors):
mysql> SELECT '10:00:00' < DATE'2024-01-01';   -- ERROR 1525 Incorrect DATE value: '10:00:00' 
ERROR 1525 (HY000): Incorrect DATE value: '10:00:00'
mysql> 
mysql> -- Column context (silent, wrong):
mysql> SELECT c, c < DATE'2024-01-01', c = DATE'2024-01-01' FROM v;
+------------+----------------------+----------------------+
| c          | c < DATE'2024-01-01' | c = DATE'2024-01-01' |
+------------+----------------------+----------------------+
| 10:00:00   |                    1 |                    0 |
| abc        |                    1 |                    0 |
| 2024-01-01 |                    0 |                    1 |
| 1          |                    1 |                    0 |
| 9999       |                    1 |                    0 |
+------------+----------------------+----------------------+
5 rows in set, 8 warnings (0.00 sec)

Sentinel semantics: a failed conversion is treated as "smaller than every DATE and not equal to anything" — violating three-valued logic (a failed conversion should yield NULL: NULL < x and NULL = x are both NULL). Note CAST('abc' AS DATE) correctly returns NULL — the conversion function itself is fine; only the comparator's conversion path is defective.

Impact: SELECT COUNT(*) FROM v WHERE c < DATE'2024-01-01' returns 4 — filtering a string column with a DATE constant silently selects every dirty/unconvertible row.

How to repeat:
CREATE TABLE v (c VARCHAR(20));
INSERT INTO v VALUES ('10:00:00'),('abc'),('2024-01-01'),('1'),('9999');

-- Constant context (strict mode — correctly errors):
SELECT '10:00:00' < DATE'2024-01-01';   -- ERROR 1525 Incorrect DATE value: '10:00:00'

-- Column context (silent, wrong):
SELECT c, c < DATE'2024-01-01', c = DATE'2024-01-01' FROM v;
-- '10:00:00' → (< = 1, = = 0)   should be NULL or an error
-- 'abc'      → (< = 1, = = 0)   should be NULL or an error
-- '1','9999' → same
-- '2024-01-01' → (< = 0) ✓ (normal row)

Thank you for the bug report.
Verified as described.