HPCC-11454 Tristate button shouldn't submit a value for default mode

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
Merge pull request #5897 from afishbeck/tristateDefault

HPCC-11454 Tristate button shouldn't submit a value for default mode

Reviewed-By: Gordon Smith <gordon.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>