Do not pollute model changes on initialisation

[bliof-fc]

This is done as in rails >= 5.2 the lock! & with_lock methods now
require that the record doesn't have any changes otherwise they'll raise
an error.

https://github.com/rails/rails/blob/v5.2.4.4/activerecord/lib/active_record/locking/pessimistic.rb#L65

      def lock!(lock = true)
        if persisted?
          if has_changes_to_save?
            raise(<<-MSG.squish)
              Locking a record with unpersisted changes is not supported. Use
              `save` to persist the changes, or `reload` to discard them
              explicitly.
            MSG
          end

          reload(lock: lock)
        end
        self
      end

Apparently clear_attribute_changes receives an array of attributes which
it should clear.

https://apidock.com/rails/v5.2.3/ActiveModel/Dirty/clear_attribute_changes

[denislavski]

🚀