Detect runaway chunks in ngx_http_parse_chunked().

As defined in HTTP/1.1, body chunks have the following ABNF:

   chunk = chunk-size [ chunk-ext ] CRLF chunk-data CRLF

where chunk-data is a sequence of chunk-size octets.

With this change, chunk-data that doesn't end up with CRLF at chunk-size
offset will be treated as invalid, such as in the example provided below:

4
SEE-THIS-AND-
4
THAT
0