Prevent crushes on parsing incorrect HTTP request

Steps to reproduce crush:
1. Start http-server (like in Ratchet's Hello World (http://socketo.me/docs/hello-world)).
2. Connect to it with telnet (instead of browser), and send any text followed by '\n\n'.
Http-server will crush with "PHP Notice:  Undefined offset: 1 in .../Guzzle/Parser/Message/MessageParser.php on line 36" (ratchet currently uses v.3.7-dev)
Merge pull request #646 from oleg8sh/patch-1

Prevent crushes on parsing an incorrect HTTP request