[#1701] don't sync chal scoring for broken chals

src/controllers/user.js

@@ -81,7 +81,7 @@ function addTask(user, task) {
 */
 
 var syncScoreToChallenge = function(task, delta){
-  if (!task.challenge || !task.challenge.id) return;
+  if (!task.challenge || !task.challenge.id || task.challenge.broken) return;
   if (task.type == 'reward') return; // we don't want to update the reward GP cost
   Challenge.findById(task.challenge.id, function(err, chal){
     if (err) throw err;