Handle already-deleted license files more gracefully

[snipe]

Edge case, but accidentally trying to delete a license file that was already deleted would trigger a 500.

[shortcut-integration]

This pull request has been linked to Shortcut Story #20451: ErrorException: Attempt to read property "filename" on null.

[what-the-diff]

• The function destroy() in LicenseFilesController.php was changed to check if the license exists before deleting a file
• A new translation string "log_does_not_exist" was added to general.php

[spencerrlongg]

Since these are soft deleted I think there's a more Eloquent ™️ way to do this using ->trashed() or something of the ilk. I can refactor like that if you'd like. This is License Files - sorry, I see.