`JSON_SEARCH` returns incorrect result for some special value

[YangKeao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

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

mysql> SELECT JSON_SEARCH('{"h": "i"}', 'all', 'i', '\\', NULL);
+---------------------------------------------------+
| JSON_SEARCH('{"h": "i"}', 'all', 'i', '\\', NULL) |
+---------------------------------------------------+
| NULL                                              |
+---------------------------------------------------+
1 row in set (0.03 sec)

3. What did you see instead (Required)

mysql> SELECT JSON_SEARCH('{"h": "i"}', 'all', 'i', '\\', NULL);
+---------------------------------------------------+
| JSON_SEARCH('{"h": "i"}', 'all', 'i', '\\', NULL) |
+---------------------------------------------------+
| "$.h"                                             |
+---------------------------------------------------+
1 row in set (0.00 sec)

4. What is your TiDB version? (Required)