HPCC-11401 Ensure strings are correctly converted to utf8 text

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #5873 from ghalliday/issue11401

HPCC-11401 Ensure strings are correctly converted to utf8 text

Reviewed-By: Jamie Noss <james.noss@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>