redirect_back causes errors when dismissing notices

Depending on the browser settings, :back might be empty.

Processing by Me::NoticesController#destroy_all as HTML
  Parameters: {"authenticity_token"=>"XXXX"}
Redirected to
Completed 500 Internal Server Error in 35ms (ActiveRecord: 20.2ms)

ActionController::RedirectBackError (No HTTP_REFERER was set in the request to this action, so redirect_to :back could not be called successfully. If this is a test, make sure to specify request.env["HTTP_REFERER"].):
  app/controllers/me/notices_controller.rb:33:in `block (2 levels) in destroy_all'
  app/controllers/me/notices_controller.rb:32:in `destroy_all'