HPCC-8656 Double nested datasets only show first "outer" row

Fixes HPCC-8656

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #3933 from GordonSmith/HPCC-8656

HPCC-8656 Double nested datasets only show first "outer" row

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>