Bugfix1: Set innodb_locks.lock_index to NOT NULL.
If a column in INFORMATION_SCHEMA table has the flag
MY_I_S_MAYBE_NULL and it is not explicitly marked as NOT NULL
with the method ::set_notnull() then it is always rendered as
NULL by MySQL.

Bugfix2: Avoid crashes if lock_index is NULL. It is NULL for table
level locks.

Pointyhat to:	Marko