fails:Enumerator::Lazy#initialize sets given size to own size if the given size is Float::INFINITY
fails:Enumerator::Lazy#initialize sets given size to own size if the given size is a Fixnum
fails:Enumerator::Lazy#initialize sets given size to own size if the given size is a Proc
fails:Enumerator::Lazy#initialize sets #size to nil if given size is nil
