Fix an infinite loop when parsing headers

Verification
 - [ ] set up an ssl server 
```ruby
tcp = TCPServer.new("127.0.0.1", 1234)
ssl = OpenSSL::SSL::SSLServer.new(tcp, OpenSSL::SSL::SSLContext.new)
ssl.accept
```
 - [ ] in another terminal, connect with RaptorIO::Protocol::HTTP::Client, without SSL
```ruby
client = RaptorIO::Protocol::HTTP::Client.new( switch_board: RaptorIO::Socket::SwitchBoard.new )
client.get("http://localhost:1234", mode: :sync)
```
 - [ ] See the server disconnect with an SSL error ("http request")
 - [ ] BEFORE: See the client spin forever
 - [ ] AFTER: raises `RaptorIO::Socket::Error::BrokenPipe` as it should