Users list: Disable button pushed beyond scroll when many groups are used

![image](https://user-images.githubusercontent.com/71468/53695932-35fd6d80-3dca-11e9-8d01-fc5b429891f8.png)

(you can see a live version on https://redash-preview.netlify.com)