Fix #dup modifying the original object

Fixes #2687

lib/carrierwave/orm/activerecord.rb

@@ -44,9 +44,9 @@ def reload(*)
         def initialize_dup(other)
           old_uploaders = _mounter(:"#{column}").uploaders
           @_mounters[:"#{column}"] = nil
+          super
           # The attribute needs to be cleared to prevent it from picked up as identifier
           write_attribute(:"#{column}", nil)
-          super
           _mounter(:"#{column}").cache(old_uploaders)
         end
 

spec/orm/activerecord_spec.rb

@@ -1960,6 +1960,12 @@ def reload(*)
       expect(new_event.image.url).to eq '/uploads/test.jpeg'
     end
 
+    it "does not modify the original object" do
+      @event.image = stub_file('test.jpeg')
+      @event.save
+      expect { @event.dup }.not_to change { @event[:image] }
+    end
+
     context "with more than one mount" do
       before do
         @uploader1 = Class.new(CarrierWave::Uploader::Base)