Fixes for NettyHttpContext

I know that my implementation of NettyHttpResponse is broken, which is leading to:

```
io.netty.handler.codec.DecoderException: java.lang.NullPointerException
	at io.netty.handler.codec.ByteToMessageDecoder.messageReceived(ByteToMessageDecoder.java:163)
	at io.netty.channel.DefaultChannelHandlerContext.invokeMessageReceived(DefaultChannelHandlerContext.java:379)
	at io.netty.channel.DefaultChannelHandlerContext.fireMessageReceived(DefaultChannelHandlerContext.java:364)
	at io.netty.channel.DefaultChannelHandlerContext.fireMessageReceived(DefaultChannelHandlerContext.java:347)
	at io.netty.channel.DefaultChannelPipeline.fireMessageReceived(DefaultChannelPipeline.java:780)
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:92)
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:489)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:464)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:358)
	at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101)
	at java.lang.Thread.run(Thread.java:680)
```

Hopefully that's something you're familiar with....