Audio Preprocessing: FFMPEG Errors result in finished Pipeline

[Alienmaster]

When FFMPEG runs into an error the job is set to "Finished".
The error should be logged in detail instead of
An error occurred while executing the PreprocessingPipeline(DocType.audio) for PreprocessingJobPayload Nl-Zandvoort_%28Gelderland%29-article.ogg! dev-celery-background-jobs-worker-1 | Error: ffprobe error (see stderr output for detail)
and the status should updated to ERROR

[Alienmaster]

The Errors weren't logged correctly which is fixed in #372 .
The pipeline itself removes broken sdocs so the pipeline ends Finished - which is correct.
This issue can be closed.