Forward RPC errors from crawler (#9569)

The `keepHTTPResponseAlive` would cause errors to be 
returned with status OK.

- Add '32' as a filler byte until a response is ready
- '0' to indicate the response is ready to be consumed
- '1' to indicate response has an error which needs
to be returned to the caller

Clear out 'file not found' errors from dir walker, since it may be 
in a folder that has been deleted since it was scanned.

cmd/peer-rest-server.go

@@ -473,7 +473,7 @@ func (s *peerRESTServer) DispatchNetOBDInfoHandler(w http.ResponseWriter, r *htt
 	ctx := newContext(r, w, "DispatchNetOBDInfo")
 	info := globalNotificationSys.NetOBDInfo(ctx)
 
-	done()
+	done(nil)
 	logger.LogIf(ctx, gob.NewEncoder(w).Encode(info))
 	w.(http.Flusher).Flush()
 }