HPCC-11821 Writes to file names without :: not working in roxie

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #6191 from richardkchapman/roxie-local-files-5

HPCC-11821 Writes to file names without :: not working in roxie

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>