If a source is deleted, the monitor page no longer shows any data

[dougkamp]

Description

If a source is deleted, the monitor page no longer shows any of the data from previous scheduled job runs for all other (non-deleted) sources

Expected behavior

When a source is deleted, the historical data in the monitor page should still be available for non-deleted sources

Steps to reproduce

Add a data source
Wait until after an execution has successfully completed
Navigate to the monitor page and view the results of the job
Add another, new data source
Delete the new data source just added
Navigate to monitor page
See error i.e. no data is shown for the source that still exists