ethstats: avoid blocking chan when received invalid stats request (#21073)

* ethstats: avoid blocking chan when received invalid stats request

* ethstats: minor code polishes

Co-authored-by: Péter Szilágyi <peterke@gmail.com>

ethstats/ethstats.go

@@ -320,8 +320,11 @@ func (s *Service) readLoop(conn *websocket.Conn) {
 			request, ok := msg["emit"][1].(map[string]interface{})
 			if !ok {
 				log.Warn("Invalid stats history request", "msg", msg["emit"][1])
-				s.histCh <- nil
-				continue // Ethstats sometime sends invalid history requests, ignore those
+				select {
+				case s.histCh <- nil: // Treat it as an no indexes request
+				default:
+				}
+				continue
 			}
 			list, ok := request["list"].([]interface{})
 			if !ok {