Update nginx-config for fallback tile

Directly-hosting-BlueMap-with-external-webservers.md

@@ -28,8 +28,9 @@ server {
     try_files $uri $uri/ =404 ;
   }
   
-  # We only want the map-tiles, so only files in the data/ folder should use this setting
+  # map-tiles are stored compressed, and they have a fallback file that should be returned if the tile does not exist
   location /data/ {
+    try_files $uri /bluemap-test/assets/emptyTile.json;
     gzip_static always;
   }