HPCC-4476 Fix KEYED substring matching against a field from the index

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4503 from ghalliday/issue4476

HPCC-4476 Fix KEYED substring matching against a field from the index

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>