fix http_chunked_gzip_decoding_error

when net::http get response as chunked gzip.

it drops last inflation. so it cause Z_BUF_ERROR.

Actually, this bug is not exist in 1.8.7, but it appears when maybe 2.x

there is test ruby code for this problems.
```ruby
require 'net/https'
require 'open-uri'

url = "http://xe.sketchbooks.co.kr/806541"
uri = URI.parse(url.to_s)
http = Net::HTTP::new(uri.host, uri.port)

http_get = Net::HTTP::Get.new(uri.request_uri)
response = http.request(http_get)
```