MM-54580: Fix panic in jobs/base_workers.go (#24631)

If GetJob fails, we would return a nil job and then try to log
with that. To prevent this, we keep a reference to the old job
and log with that in the error case.

https://mattermost.atlassian.net/browse/MM-54580

```release-note
Fix a panic where a simple worker would crash if if failed to get a job.
```

server/channels/jobs/jobs_test.go

@@ -38,6 +38,7 @@ func makeJobServer(t *testing.T) (*JobServer, *storetest.Store, *mocks.MetricsIn
 		ConfigService: configService,
 		Store:         mockStore,
 		metrics:       mockMetrics,
+		logger:        mlog.CreateConsoleTestLogger(t),
 	}
 
 	return jobServer, mockStore, mockMetrics