use "_isInteractionComplete" instead of "_isComplete"

_isComplete is true when the component was solved before and the course get's relaunched
_isInteractionComplete is true when no more attempts are left or the component gets solved correctly, but get's set to false when course is reloaded

js/adapt-contrib-slider.js

@@ -262,7 +262,7 @@ define([
             event.preventDefault();
             this.tempValue = false;
 
-            if (this.model.get('_isComplete')) {
+            if (this.model.get('_isInteractionComplete')) {
               return;
             }