The external 'for' loop in remove_dup_with_compare() handled 
HA_ERR_RECORD_DELETED by just starting over without advancing 
to the next record which caused an infinite loop. 
 
This condition could be triggered on certain data by a SELECT 
query containing DISTINCT, GROUP BY and HAVING clauses. 

Fixed remove_dup_with_compare() so that we always advance to 
the next record when receiving HA_ERR_RECORD_DELETED from 
rnd_next().