Bug 11549: [follow-up] Make NewOrder calculate new parent_ordernumber

Bug 11549: [follow-up] Make NewOrder calculate new parent_ordernumber

If parent_ordernumber is not set in NewOrder parameter, it is
automatically set to ordernumber.

This patch only avoid code duplication.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
This solution is better!

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes all tests and QA script. Also all tests in
t/db_dependent/Acquisitions/.

Confirmed bug and that the patch fixes it.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>