`httpc:request` returns `nil, nil` on response with broken status line

To reproduce the bug, run:

```bash
echo TEAPOT/1.1 | nc -lp 1337
```

```lua
local http = require "resty.http"
local httpc = http.new()
local res, err = httpc:request_uri("http://127.0.0.1:1337")
assert(res or err, "there must be either a result or an error")
```
