lib/webrick/log.rb: sanitize any type of logs

	It had failed to sanitize some type of exception messages.  Reported and
	patched by Yusuke Endoh (mame) at https://hackerone.com/reports/223363

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@59898 b2dd03c8-39d4-4d8f-98ff-823fe69b080e