Subselect's engine checks table->status field to determine if the
record was properly found when we use keyread upon the table.
Partition engine checks all the partitions for given key
before return. So if matching record was found in the first
partition and no matching records were found in the second, 
we have table->status == NOT_FOUND after the function, what
makes subselects to skip matching records.
The patch adds table->status= 0 if we actually found something.