feed controller: return service unavailable if feed isn't loaded

http-service/src/main/java/net/runelite/http/service/feed/FeedController.java

@@ -38,6 +38,7 @@ import net.runelite.http.service.feed.osrsnews.OSRSNewsService;
 import net.runelite.http.service.feed.twitter.TwitterService;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.CacheControl;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.scheduling.annotation.Scheduled;
 import org.springframework.web.bind.annotation.GetMapping;
@@ -122,7 +123,8 @@ public class FeedController
 	{
 		if (memoizedFeed == null)
 		{
-			return ResponseEntity.notFound()
+			return ResponseEntity.status(HttpStatus.SERVICE_UNAVAILABLE)
+				.cacheControl(CacheControl.noCache())
 				.build();
 		}