JobMaintenanceServiceImpl stops if a job definition is not registered

[longma1]

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Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

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2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
If a job instance with a non-registered job definition is being processed, this will throw an exception and stop the the maintenance cycle of jobs after it, the service should throw out a warning but continue to the next job instance.