fix bugs of decode while polling

src/main/java/com/corundumstudio/socketio/protocol/PacketDecoder.java

@@ -63,7 +63,13 @@ public class PacketDecoder {
             // skip "d="
             packet = packet.substring(2);
         }
-        packet = new String(packet.getBytes(CharsetUtil.ISO_8859_1), CharsetUtil.UTF_8);
+
+	/**
+	 * this line will convert some utf-8 characters to "?"
+	 *
+	 * @see https://github.com/mrniko/netty-socketio/issues/515
+	 */
+        // packet = new String(packet.getBytes(CharsetUtil.ISO_8859_1), CharsetUtil.UTF_8);
 
         return Unpooled.wrappedBuffer(packet.getBytes(CharsetUtil.UTF_8));
     }