Fix attempt to set created_at for a document that has already been de…

…leted

lib/mongoid/timestamps/created.rb

@@ -22,7 +22,7 @@ module Created
       # @example Set the created at time.
       #   person.set_created_at
       def set_created_at
-        if !timeless? && !created_at
+        if !timeless? && !created_at && !frozen?
           time = Time.configured.now
           self.updated_at = time if is_a?(Updated) && !updated_at_changed?
           self.created_at = time