fix poll unvoting

lib/channel/poll.js

@@ -65,6 +65,13 @@ PollModule.prototype.onUserPostJoin = function (user) {
     user.socket.on("closePoll", this.handleClosePoll.bind(this, user));
 };
 
+PollModule.prototype.onUserPart = function(user) {
+    if (this.poll) {
+        this.poll.unvote(user.ip);
+        this.sendPollUpdate(this.channel.users);
+    }
+};
+
 PollModule.prototype.sendPoll = function (users) {
     if (!this.poll) {
         return;