io.c: get src_size from stp. Fix r66995.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66996 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
io.c: get src_size from stp. Fix r66995.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66996 b2dd03c8-39d4-4d8f-98ff-823fe69b080e