Fixes an issue where cache sweepers with only after filters would hav…

…e no controller object

It would raise undefined method controller_name for nil

actionpack/lib/action_controller/caching/sweeping.rb

@@ -61,6 +61,7 @@ def before(controller)
         end
 
         def after(controller)
+          self.controller = controller
           callback(:after) if controller.perform_caching
           # Clean up, so that the controller can be collected after this request
           self.controller = nil