zlib.c: return unshared string
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45625 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
zlib.c: return unshared string
since it cannot be shared ever.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45625 b2dd03c8-39d4-4d8f-98ff-823fe69b080e