Tile server does not consistently add `Access-Control-Allow-Origin` headers

[iwakureal]

I use ORM's tile overlays frequently in Google Earth and I have recently noticed it's often been struggling to load the tiles. I go to the developer console and I'm greeted with hundreds of CORS errors, No 'Access-Control-Allow-Origin' header is present on the requested resource. In the Network tab I saw that some of the tile requests indeed did not have the Access-Control-Allow-Origin: * that I saw in most of them, and I believe they also had HTTP 304 Not Modified for their response codes. When I used an extension to unlock CORS, the errors disappeared but it still could not load tiles any better. I feel like this is a server configuration issue so not sure where else to reasonably put this lol.

[Nakaner]

Unfortunately, the server returned that header for successful (2xx) requests only. I fixed it (I hope).

Reason: https://serverfault.com/questions/690199/how-do-i-add-no-cache-headers-to-all-404-pages-served-by-apache-and-nginx