Fix client not found bug.

src/main/java/com/corundumstudio/socketio/transport/WebSocketTransport.java

@@ -83,6 +83,13 @@ public class WebSocketTransport extends BaseTransport {
         } else if (msg instanceof TextWebSocketFrame) {
             TextWebSocketFrame frame = (TextWebSocketFrame) msg;
             WebSocketClient client = channelId2Client.get(ctx.channel());
+            if (client == null) {
+                log.debug("Client with was already disconnected. Channel closed!");
+                ctx.channel().close();
+                frame.release();
+                return;
+            }
+
             ctx.pipeline().fireChannelRead(new PacketsMessage(client, frame.content()));
             frame.release();
         } else if (msg instanceof FullHttpRequest) {

src/main/java/com/corundumstudio/socketio/transport/XHRPollingTransport.java

@@ -87,8 +87,11 @@ public class XHRPollingTransport extends BaseTransport {
             QueryStringDecoder queryDecoder = new QueryStringDecoder(req.getUri());
 
             if (queryDecoder.path().startsWith(path)) {
-                handleMessage(req, queryDecoder, ctx);
-                req.release();
+                try {
+                    handleMessage(req, queryDecoder, ctx);
+                } finally {
+                    req.release();
+                }
                 return;
             }
         }