Handle case where jobset has no defined errormsg for api/jobsets

Dependencies

• [2] NGFKXI5F Add `haserrormsg` boolean attribute to jobset API response
• [3] FRTDCC6I Extend the jobset API response
• [4] BKOIYITR added some json responses

Change contents

• replacement in src/lib/Hydra/Controller/API.pm at line 91
  [2.41]→[2.41:115](∅→∅)
  − haserrormsg => $jobset->errormsg eq "" ? JSON::false : JSON::true
  [2.41]

  [3.2922]
  + haserrormsg => defined($jobset->errormsg) ? ($jobset->errormsg eq "" ? JSON::false : JSON::true) : JSON::false