WEBrick: prevent response splitting and header injection

	This is a follow up to d9d4a28f.
	The commit prevented CRLR, but did not address an isolated CR or an
	isolated LF.

Co-Authored-By: NARUSE, Yui <naruse@airemix.jp>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_6@67808 b2dd03c8-39d4-4d8f-98ff-823fe69b080e