Fix a "Argument isn't numeric" warning if there are not jobsets

Dependencies

• [2] JY7BXXOP Split viewing and editing a project
• [3] 3PNG7NIB Remove trailing whitespace
• [*] 7YBYT2LQ

Change contents

• replacement in src/root/project.tt at line 30
  [2.2863]→[2.2863:2901](∅→∅)
  − [% IF project.jobsets.size > 0 %]
  [2.2863]

  [2.2901]
  + [% IF project.jobsets %]