security fix, anon should not be treated as though they can create anything

spec/models/category_spec.rb

@@ -67,14 +67,15 @@ describe Category do
       can_post_category.save
 
       Category.post_create_allowed(guardian).count.should == 3
+
+      # anonymous has permission to create no topics
+      guardian = Guardian.new(nil)
+      Category.post_create_allowed(guardian).count.should == 0
+
     end
 
   end
 
-  describe "post_create_allowed" do
-
-  end
-
   describe "security" do
     let(:category) { Fabricate(:category) }
     let(:category_2) { Fabricate(:category) }