fix bug when user not signed in

Signed-off-by: Matheus Agio Nerone <man13@inf.ufpr.br>

app/controllers/learning_objects_controller.rb

@@ -13,7 +13,7 @@ class LearningObjectsController < ApplicationController
   # GET /learning_objects/1
   # GET /learning_objects/1.json
   def show
-    @liked = learning_object_repository.liked?(current_user, @learning_object)
+    @liked = learning_object_repository.liked?(current_user, @learning_object) if user_signed_in? 
   end
 
   # GET /learning_objects/new

app/views/learning_objects/show.html.erb

@@ -61,6 +61,7 @@
         </div>
       </div>
       <div class="rating-panel">
+        <% if user_signed_in? %>
         <div class="actions">
           <div class="col-md-3 action">
             <%= link_to like_learning_object_path(id: @learning_object.id), class: 'vote',method: :post, remote: true do %>