HTTP Chunk, wrong delimiter written

CRLF_BUF is being created from ZERO_CRLF rather than CRLF.

This has the effect of appending a 0 to every chunked HTTP content. 

Below is a diff of the trace of two curl requests to a simple Netty Http Server which echoes input back to the client. The text sent is "hello". The first request is against 4.0.7-final, the second against 4.0.8-final.

In both cases the request header "Accept-Encoding: gzip" is sent. Curl barfs on 4.0.8-final request presumably because it recognises that the content isn't encoded correctly.

```
Recv data, 47 bytes (0x2f)
Recv data, 49 bytes (0x31)

42,47c42,47
< 0004: ...........H.........
< 001b: a
< 001e: .....6....
< 002a: 0
< 002d:
Info: Connection #0 to host 127.0.0.1 left intact

 > 0004: ...........H.........0
 > 001c: a
 > 001f: .....6....0
 > 002c: 0
 > 002f:
Info: Problem (3) in the Chunked-Encoded data
```