HPCC-8922 Fix problems casting constant decimals to booleans

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4060 from ghalliday/issue8922

HPCC-8922 Fix problems casting constant decimals to booleans

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>