/v1/actions/*: return 404 if no objects found

[Al2Klimov]

... and not 500.

fixes #7956

[yhabteab]

Before:

Command: # curl -k -v -u root:icinga -H 'Accept: application/json' -X POST 'https://localhost:5665/v1/actions/add-comment' -d '{ "type": "Host", "filter": "host.name==\"test\"", "author": "user", "comment": "Some comments here"}'

POST /v1/actions/add-comment HTTP/1.1
Host: localhost:5665
Authorization: Basic cm9vdDppY2luZ2E=
User-Agent: curl/7.58.0
Accept: application/json
Content-Length: 102
Content-Type: application/x-www-form-urlencoded

* upload completely sent off: 102 out of 102 bytes
HTTP/1.1 500 Internal Server Error

After:

POST /v1/actions/add-comment HTTP/1.1
Host: localhost:5665
Authorization: Basic cm9vdDppY2luZ2E=
User-Agent: curl/7.58.0
Accept: application/json
Content-Length: 102
Content-Type: application/x-www-form-urlencoded

* upload completely sent off: 102 out of 102 bytes
HTTP/1.1 404 Not Found

[Al2Klimov]

@cla-bot check