Fix crash if the details tab in the job view is clicked with no jobs present

This MR contains a bug fix for a crash: if no jobs are defined and the user clicks in (or types into) the empty "Details" tab on the left side beneath the job selector, the application crashed.

requested review from @m.puchner

assigned to @m.puchner

approved this merge request

assigned to @t.knopff and unassigned @m.puchner

merged

mentioned in commit f9bd08ed