Fix the TODO parser

The last TODO elem was almost always left out from the returned value for simple use cases.

Try the code out with this:
```
console.log(enml.TodosOfENML(''
  + '<?xml version="1.0" encoding="UTF-8"?>'
  + '<!DOCTYPE en-note SYSTEM "http://xml.evernote.com/pub/enml2.dtd">'
  + '<en-note>'
    + '<div>Some stuff</div>'
    + '<div><en-todo></en-todo>first todo elem</div>'
    + '<div><en-todo></en-todo>second todo elem<br clear="none"/></div>'
    + '<div><en-todo checked="true"></en-todo>third todo elem</div>'
  + '</en-note>'
));
```

The original code left out the "third todo elem", because basically it was the last elemen, and there were no code to push it into the returned values.
I made a quick fix. And sorry to say but I think this codebase could use a rewrite, because it looks like it was put together in a hurry. :\