Fixes #11509. Implement a) detection of broken 'split PDF to JPEG', b) fire...

Fixes #11509. Implement a) detection of broken 'split PDF to JPEG', b) fire 'pdf repair'. Also implement configuration von 'convert' and 'pdf2svg'
3 jobs for B11509-PDF-splitting-fails in 6 minutes and 47 seconds (queued for 2 seconds)