HTTP returns codes incorrect for some endpoints

[gb-beng]

Example where we would expect a 400

$  curl --include https://data.beeldengeluid.nl/gtaa/invalid
HTTP/1.1 200 OK
Date: Thu, 23 Jun 2022 13:37:11 GMT
Server: nginx/1.14.1
Content-Type: application/ld+json
Content-Length: 174
Access-Control-Allow-Origin: *

[
  {
    "@id": "http://data.beeldengeluid.nl/gtaa/invalid",
    "https://schema.org/publisher": [
      {
        "@id": "https://www.beeldengeluid.nl/"
      }
    ]
  }
]

Example where we would expect a 404

$ curl --include https://data.beeldengeluid.nl/gtaa/99999999999999999999999999999999999999
HTTP/1.1 200 OK
Date: Thu, 23 Jun 2022 13:37:14 GMT
Server: nginx/1.14.1
Content-Type: application/ld+json
Content-Length: 205
Access-Control-Allow-Origin: *

[
  {
    "@id": "http://data.beeldengeluid.nl/gtaa/99999999999999999999999999999999999999",
    "https://schema.org/publisher": [
      {
        "@id": "https://www.beeldengeluid.nl/"
      }
    ]
  }
]

[gb-beng]

Slightly related: #220 .