Bug 22390: (bug 15184 follow-up) Use aqorders.subscriptionid instead of biblio.serial

Bug 22390: (bug 15184 follow-up) Use aqorders.subscriptionid instead of biblio.serial

It seems that we made a wrong assumption on bug 15184, see
  commit d658cb6f7ecb18845a78d4708ee63ad1126f220f
  Bug 15184: Do copy items for not a serial OR if items are created on ordering

To know if an order has been created from a subscription we should check
$order->subscriptionid instead of the $biblio->serial flag

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>