HPCC-10383 IE8 Issue with TreeMap and set "selectedItems"

Fixes HPCC-10383

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #5120 from GordonSmith/HPCC-10383

HPCC-10383 IE8 Issue with TreeMap and set "selectedItems"

Reviewed-By: Miguel Vazquez <miguel.vazquez@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>