Don't winnow results when search is empty

@pfiller Here's a better (working) solution to the winnow_results performance. It no longer winnows when first opening the select.

**Before change (5000 items)**
![screen shot 2013-05-21 at 9 28 47 am](https://f.cloud.github.com/assets/127289/542720/49c3f56e-c229-11e2-95a4-192b55ac9e74.png)

**After change**
![screen shot 2013-05-21 at 9 53 40 am](https://f.cloud.github.com/assets/127289/542731/7d6be4ee-c229-11e2-9b46-94f71ca7d6d9.png)

Note: The big numbers in the second screenshot represent actual searching. The rest are just opening the select.