If the new or already existing job fails on calculation (with JobStatus::Failed), then JobPropertiesWidget will switch to the Message tab.
If the datafield exists, all its values will be set to 0.0. This looks as white (no datafield) or dark blue (values = 0.0) color map.
So a job failure will hardly pass unnoticed even without a popup window.
If some datafiles are missing, then on project opening user will see such window and details will be provided in the Message tab for corresponding jobs.
