#392 When postgres conncetion is lost/terminated DPR hangs

[margotc]

Testing revealed that loss of database connection mid step on processing
jobs causes DPR to hang and the user would be unable to shut it down except
through task manager. This behaviour was found in the following
circumstances:

- postgresql connection was terminated prior to PF Checksum validation
starting - no error was presented
- postgresql connection was terminated after 'Extra files found' dialogue
popped up - in this case error was presented, but DPR hung and had to be
stopped using task manager