Filter join and leave websocket messages

views/include/websocket.html

@@ -10,6 +10,9 @@
             ws.onmessage = function(e) {
                 var firstColon = e.data.indexOf(":");
                 if(firstColon === -1) {
+                    if(e.data.startsWith("+") || e.data.startsWith("-")) {
+                        return;
+                    }
                     set_error("{{=T('Invalid WebSocket data received')}}: '" + e.data + "'");
                     return;
                 }