If item->cached_table is set, find_field_in_tables() returns found field
even if it doesn't belong to current select. Because Item_field::fix_fields
doesn't expect such behaviour, reported bug occurs.

Item_field::fix_fields() was modifed to detect when find_field_in_tables() 
can return field from outer select and process such fields accordingly.
In order to ease this code which was searching and processing outed fields was
moved into separate function called Item_field::fix_outer_field().