Bug in logic for handling error messages when entity IDs are missing in Item `POST` endpoint

[VKTB]

Sending the following request:

curl -X 'POST' \
  'http://localhost:8000/v1/items' \
  -H 'accept: application/json' \
  -H 'Content-Type: application/json' \
  -d '{
  "catalogue_item_id": "string",
  "system_id": "string",
  "is_defective": true,
  "usage_status_id": "string"
}'

returns:

{
  "detail": "The specified system does not exist"
}

even though the checks for the catalogue_item_id and usage_status_id happen before the system_id check.