Error code 404 if SiteDefinitionApiEnabled is false

Description

Steps to reproduce:

1. Disable SiteDefinitionApiEnabled settings in code:

            var contentApiOptions = new ContentApiOptions
            {
                SiteDefinitionApiEnabled = false
            };

2. Send a GET request:

{{EPCMSHost}}/api/episerver/v1.0/site

Expected:
Returns error code 403 Forbidden.

Actual:
Returns error code 404 Not Found - this causes confusion that there is no site data in the CMS.

    "error": {
        "code": "NotFound",
        "message": "Not Found"
    }