Check that the array key exists in the label engine

[snipe]

This fixes a 500 that would occur in very unusual circumstance, but we'd occasionally see it on the demo.

[shortcut-integration]

This pull request has been linked to Shortcut Story #25186: ErrorException: Undefined array key 1 in /home/serverpilot/apps/develop.snipeitapp.com/snipe-it/app/Http/Controllers/LabelsController.php:76.

[what-the-diff]

PR Summary

• Improved error prevention in Label Controller
  Certain actions in our system were performed without necessary checks, which could lead to unexpected behaviors or errors. This change ensures operations occur only when specific conditions are fulfilled, enhancing the system's reliability.