hydra-eval-jobset: fix use of uninitialized value

Dependencies

• [2] QGLBQ5IO Remove hydra-eval-guile-jobs
• [3] Q6VFUIC6 Remove hydra-eval-guile-jobs
• [4] QMW24O5S Add support for Guile & Guix.
• [5] LPPZS34Y Merge remote-tracking branch 'origin/master' into flake
• [6] 5SHCWE7X * Prevent repeated evaluation of a jobset with the same inputs. This
• [7] RXVJFQ5A Evaluator cleanups
• [*] N22GPKYT * Put info about logs / build products in the DB.

Change contents

• replacement in src/script/hydra-eval-jobset at line 647
  [3.2206]→[2.1524:1612](∅→∅)
  − my @args = ($jobset->nixexprinput, $jobset->nixexprpath, inputsToArgs($inputInfo));
  [3.2206]

  [3.2294]
  + my @args = ($jobset->nixexprinput // "", $jobset->nixexprpath // "", inputsToArgs($inputInfo));