Intend to backport OAK-6391 - With FastQuerySize, getSize() returns -1 if there are exactly 21 rows

[Thomas Mueller]

Hi,
    
I'd like to backport OAK-6391 to the maintenance branches. The query result 
getSize() method is often used, and it is important that the result is as 
accurate as possible (even though the spec allows to return -1).

Regards,
Thomas