io.c: check null char
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60097 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
io.c: check null char
on the patch by tommy (Masahiro Tomita) in [ruby-dev:50272].
[Bug #13960]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60097 b2dd03c8-39d4-4d8f-98ff-823fe69b080e