[BUG] Job progress bar does not reach 100% for idle processes

[MBartkowiakSTFC]

Description of the error
Normally, a job should reach 100% when it is finished. However, if more processes than necessary are created in multiprocessing mode, it can happen that 100% is not reached.

Describe the expected result
For a trajectory with a single molecule, Infrared analysis in multiprocessing mode should reach 100% when finished.

Describe the actual result
The job table was showing 0% and 'Finished' at the end of the run.

Suggested fix
One sensible solution would be not to create more processes than there are analysis steps to be run.

Additional details
N/A