This bug could affect queries with IN subqueries in WHERE clause and using
derived tables to which split optimization potentially could be applied.

When looking for the best split of a splittable derived table T any key
access from a semi-join materialized table used for lookups S to table T
must be excluded from consideration because in the current implementation
of such tables as S the values from its records cannot be used to access
other tables.

Approved by Oleksandr Byelkin <sanja@mariadb.com>