SUP-2961, Dashboard: Active challenges not showing on dashboard after user unregisters

-- Fixed and adde unit tests

Author: vikasrohit

app/services/challenge.service.js

@@ -80,7 +80,7 @@
 
               // if user has role of observer
               var roles = _.get(challenge, 'userDetails.roles', []);
-              if (roles.length > 0) {
+              if (roles && roles.length > 0) {
                 var submitterRole = _.findIndex(roles, function(role) {
                   var lRole = role.toLowerCase();
                   return lRole === 'submitter';