NQF Highlighting bugfix

**Story:** https://www.pivotaltracker.com/story/show/62175964

For measures, such as 0031, sometimes the logic highlighting throws a TypeError for undefined length.

I updated the highlighting logic in result.js.coffee to check if there are existing preconditions to recurse on.

### Error on patient-select ###
![original_typeerror](https://f.cloud.github.com/assets/456952/1744720/606af98e-6422-11e3-91d2-e0230bbf58f7.png)

### Post bugfix ###
![post_bugfix](https://f.cloud.github.com/assets/456952/1744721/6331ef7e-6422-11e3-9a20-6179c3bc64dd.png)

I am unsure if this affects the highlighting logic in a specific way, so that is the primary feedback I am looking for, etc.