4018 Notes on multichaptered drafts causing errors

https://code.google.com/p/otwarchive/issues/detail?id=4018

If a chaptered draft had notes, you'd get the error, "Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id." This was on line `<% endnotes_link = link_to (@work.notes.blank? ? ts("notes") : ts("more notes")), get_endnotes_link %>` due to the `get_endnotes_link` method:
```
  def get_endnotes_link
    current_page?(:controller => 'chapters', :action => 'show') ?
      chapter_path(@work.last_posted_chapter.id, :anchor => 'work_endnotes') :
      "#work_endnotes"
  end
```
26 & 27 are the changes here -- make sure this chapter is the last chapter, and by last chapter, we mean "last posted chapter if the work is posted, otherwise, just use the last chapter that exists."