socket.c: null byte at Socket.getnameinfo

	* ext/socket/socket.c (sock_s_getnameinfo): check null byte.
	  patched by tommy (Masahiro Tomita) in [ruby-dev:50286].
	  [Bug #13994]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@62948 b2dd03c8-39d4-4d8f-98ff-823fe69b080e