Stop slide toggle when toggled

Stop slide toggle when toggled

Hi i'm working on a site which requires a new form field to become available once the other radio button has been selected. I've got a slide toggle to work when this is selected but if i were to click the radio button again it performs the slideup action.

Is there anyway to stop the slideup action happening if the toggled element is clicked again? i only want it to slide back up if the other radio buttons are selected. Heres my fiddle  http://jsfiddle.net/e08jo9gr/6/

Help much appreciated.