HPCC-9558 Spot and handle deleted WU

Prevents ECL Watch from displaying toaster exceptions for deleted WUs.

Fixes HPCC-9558

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #4553 from GordonSmith/HPCC-9558-Spot_Del_WU

HPCC-9558 Spot and handle deleted WU

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>