Assertion `pos != (~(my_off_t) 0)` fails in `my_seek()` during UPDATE with EXCEPT subquery

## Affected version - MariaDB `11.8.8-MariaDB-debug` - Source revision: `46a8eb42a520193686d9a16d4cea4b3e002917e4` ## Summary The server aborts while executing an `UPDATE` statement whose assigned expression is an `IN` predicate over an `EXCEPT` subquery: ```sql UPDATE v0 SET v1 = v1 IN (SELECT v1 FROM v0 AS v6 EXCEPT SELECT v1 FROM v0); ``` The failing assertion is in `my_seek()`: ```text mariadbd: /home/mysql/mariadb/mysys/my_seek.c:53: my_off_t my_seek(File, my_off_t, int, myf): Assertion `pos != (~(my_off_t) 0)' failed. ``` The stack includes temporary row deletion: ```text my_seek() unlink_deleted_block() delete_dynamic_record() handler::ha_delete_tmp_row(unsigned char*) select_unit::send_data(...) ... Item_in_subselect::val_bool() Item::save_bool_in_field(...) multi_update::send_data(...) Sql_cmd_update::execute_inner(...) ``` This points to an invalid temporary-row file position during set-operation execution. ## Steps to reproduce Run the following SQL against a debug build: ```sql SET GLOBAL TRANSACTION READ WRITE; SET SESSION TRANSACTION READ WRITE; DROP DATABASE IF EXISTS test_sqlright1; CREATE DATABASE IF NOT EXISTS test_sqlright1; USE test_sqlright1; CREATE TABLE v1099(c1100 INT); CREATE TABLE v0 (v1 TEXT(83)); INSERT INTO v0 (v1) VALUES (51); UPDATE v0 SET v1 = (   SELECT 94   FROM (     SELECT v1 AS v5     FROM v0 AS v4     GROUP BY v1     HAVING v1     EXCEPT     SELECT v1 FROM v0   ) AS v3,   v0 AS v2   JOIN v0 ); INSERT INTO v0 (v1) VALUES   (61),   (     v1 + (       SELECT v1       WHERE (32880467.000000 * v1 * -1 IN (30, -1, 48, 0, -1))       GROUP BY v1       ORDER BY v1 / v1, v1 + v1     )   ); UPDATE v0 SET v1 = v1 IN (   SELECT v1 FROM v0 AS v6   EXCEPT   SELECT v1 FROM v0 ); ``` ## Actual result The server aborts: ```text Assertion `pos != (~(my_off_t) 0)' failed. got signal 6 my_seek() handler::ha_delete_tmp_row(unsigned char*) select_unit::send_data(...) Item_in_subselect::val_bool() Sql_cmd_update::execute_inner(...) Query: UPDATE v0 SET v1 = v1 IN ( SELECT v1 FROM v0 AS v6 EXCEPT SELECT v1 FROM v0 ) ``` After replay: ```text server_ready 1 client_rc 0 server_alive_after 0 ```