allow multiple taxons in product

Allow to affect multiple taxons in product when using spree-multi-domain : see spree-contrib#148

app/controllers/spree/admin/products_controller_decorator.rb

@@ -1,17 +1,18 @@
 Spree::Admin::ProductsController.class_eval do
   update.before :set_stores
+  before_action :find_stores, only: [:update]
 
-  def update
+  private
+
+  def set_stores
+    @product.store_ids = nil unless params[:product].key? :store_ids
+  end
+
+  def find_stores
     store_ids = params[:product][:store_ids]
     if store_ids.present?
       params[:product][:store_ids] = store_ids.split(',')
     end
-    super
   end
 
-  private
-
-  def set_stores
-    @product.store_ids = nil unless params[:product].key? :store_ids
-  end
 end