dict_set_corrupted(): Use the canonical way of searching for
less-than-equal (PAGE_CUR_LE) and then checking low_match.

The code that was introduced in MySQL 5.5.17 in
    Bug#11830883 SUPPORT "CORRUPTED" BIT FOR INNODB TABLES AND INDEXES
could position the cursor on the page supremum, and then attempt
to overwrite non-existing 7th field of the 1-field supremum record.

Approved by Jimmy Yang