io.c: fix race between read and close
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57199 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
io.c: fix race between read and close
the IO gets closed before the reading thread achieve the lock.
[ruby-core:78845] [Bug #13076]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57199 b2dd03c8-39d4-4d8f-98ff-823fe69b080e