Always show resend button when viewing an order

Even for guest orders

Fixes spree#2318

core/app/views/spree/admin/orders/edit.html.erb

@@ -1,7 +1,7 @@
 <%= csrf_meta_tags %>
 <% content_for :page_actions do %>
   <li><%= event_links %></li>
-  <li><%= button_link_to t(:resend), resend_admin_order_url(@order), :method => :post, :icon => 'icon-email' if @order.user %></li>
+  <li><%= button_link_to t(:resend), resend_admin_order_url(@order), :method => :post, :icon => 'icon-email' %></li>
   <li><%= button_link_to t(:back_to_orders_list), admin_orders_path, :icon => 'icon-arrow-left' %></li>
 <% end %>