Unexpected result of IFNULL and LIKE functions

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

In the following test case, `t0.c0` has one not null value, so the IFNULL function should return `t0.c0`, then the LIKE function should return true. However, it returns false. In the prepared statement, it can produce a correct result:

```
CREATE TABLE t0(c0 DECIMAL NOT NULL);
INSERT INTO t0 VALUES (-1324907974);
SELECT ((IFNULL(t0.c0, 'k'))LIKE(t0.c0)) FROM t0; -- 0
SET @c = 'k';
PREPARE prepare_query FROM 'SELECT ((IFNULL(t0.c0, ?))LIKE(t0.c0)) FROM t0';
EXECUTE prepare_query USING @c; -- 1
```

### 2. What did you expect to see? (Required)

The normal query should have the same result with the prepared statement.

### 3. What did you see instead (Required)

The normal query has wrong result.

### 4. What is your TiDB version? (Required)

Release Version: v9.0.0-beta.2.pre-196-g312226f869\nEdition: Community\nGit Commit Hash: 312226f869d56922135e1c177cac6c90319c3134\nGit Branch: HEAD\nUTC Build Time: 2025-09-21 08:27:14\nGoVersion: go1.23.11\nRace Enabled: false\nCheck Table Before Drop: false\nStore: unistore\nKernel Type: Classic