Handle errors in /task/list

public/js/main.js

@@ -213,9 +213,13 @@ $(function() {
 
         $.get(url)
             .done(function(tasksJson) {
+                if (tasksJson.error){
+                    self.error(tasksJson.error);
+                }else{
                     for (var i in tasksJson){
                         self.tasks.push(new Task(tasksJson[i].uuid));
                     }
+                }
             })
             .fail(function() {
                 self.error(url + " is unreachable.");