Fixed this={} in processDbResult

[Solpatium]

this in processDbResult in save-job.js file is always {}, but it should be bound to agenda instance. Because of this a job is never run immediately, which is not a big issue, but it raises an error, for example, after Babel transpilation, because this is undefined.

Fixing it breaks the tests, because

processJobs.call(this, job);

might actually run and it doesn't take _jobsToLock into consideration. This is why a check for this was added.

[Beretta1979]

Could this be reviewed , need this fix

[mkaput]

rebased onto latest master