set encoder to null every time we write a new HttpMessage in case there is no encoder to be used for the message

Author: Felix Trepanier

src/main/java/org/jboss/netty/handler/codec/http/HttpContentEncoder.java

@@ -94,6 +94,7 @@ public void writeRequested(ChannelHandlerContext ctx, MessageEvent e)
         } else  if (msg instanceof HttpMessage) {
             HttpMessage m = (HttpMessage) msg;
 
+            encoder = null;
             String encoding;
             if(msg instanceof HttpResponse) {
                 // Determine the content encoding.