Check room exists before removing user.

src/app.js

@@ -123,7 +123,9 @@ function onJoin(data, bot) {
 }
 
 function onLeave(data, bot) {
-	bot.rooms[data.roomId].users = bot.rooms[data.roomId].users.filter((userId) => userId !== data.userId);
+	if (bot.rooms[data.roomId]) {
+		bot.rooms[data.roomId].users = bot.rooms[data.roomId].users.filter((userId) => userId !== data.userId);
+	}
 }
 
 function onMessage(message, bot, games) {