fix(WS): a socket could join the same room multiple times

backend/logic/ws.js

@@ -294,7 +294,7 @@ class _WSModule extends CoreClass {
 		return new Promise(resolve => {
 			// create room if it doesn't exist, and add socketId to array
 			if (WSModule.rooms[room]) {
-				if (!(socketId in WSModule.rooms[room])) WSModule.rooms[room].push(socketId);
+				if (WSModule.rooms[room].indexOf(socketId) === -1) WSModule.rooms[room].push(socketId);
 			} else WSModule.rooms[room] = [socketId];
 
 			return resolve();