add clause for websocket close code 4537 because why?

handlers.go

@@ -96,6 +96,7 @@ func (rl *Relay) HandleWebsocket(w http.ResponseWriter, r *http.Request) {
 					websocket.CloseGoingAway,        // 1001
 					websocket.CloseNoStatusReceived, // 1005
 					websocket.CloseAbnormalClosure,  // 1006
+					4537,                            // some client seems to send many of these
 				) {
 					rl.Log.Printf("unexpected close error from %s: %v\n", r.Header.Get("X-Forwarded-For"), err)
 				}