* lib/fileutils.rb (fu_get_uid, fu_get_gid): Etc.getpwnam/getgrnam may
  returns nil.

* lib/webrick/utils.rb (su): ditto.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45712 b2dd03c8-39d4-4d8f-98ff-823fe69b080e