revid:mattias.jonsson@oracle.com-20131119103616-u6t82s8cpgp0q3ex

Use of uninitialized memory in the priority queue used for returning records
in sorted order.

It happens if no previous partition have returned a row since the
beginning of index_init + an index_read* call returned
HA_ERR_KEY_NOT_FOUND for all partitions (otherwise the record
buffer/priority queue would be initialized) + an index_next/prev
call where all partitions returns HA_ERR_END_OF_FILE.