HPCC-10253 WsWorkunits::onGet should return exceptions to the client

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
Merge pull request #5024 from afishbeck/wswu-onget-exceptions

HPCC-10253 WsWorkunits::onGet should return exceptions to the client

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>