HPCC-9728 Unordered multi core join helper not working

Due to a simple bug, the unordered version of the multi core
join helper output no rows.
[As enabled with ,HINT(parallel_match), HINT(unsorted_output)]

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge branch 'hpcc-9728' into candidate-4.0.2

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>