[FIX] l10n_be_intrastat: get location_id from stock move

purchase.order have been rewritten with cb01be2

It was not taken into account for intrastat  who still used the now not
existing "location_id" on purchase order.

This commit use instead the method _get_destination_location which
should be equivalent.

opw-677497

addons/l10n_be_intrastat/wizard/xml_decl.py

@@ -230,9 +230,9 @@ class xml_decl(osv.TransientModel):
                 poline_ids = POL.search(
                     cr, uid, [('invoice_lines', 'in', inv_line.id)], context=context)
                 if poline_ids:
-                    purchaseorder = POL.browse(cr, uid, poline_ids[0], context=context).order_id
+                    purchaseorder = POL.browse(cr, uid, poline_ids, context=context).order_id
                     region_id = warehouse_mod.get_regionid_from_locationid(
-                        cr, uid, purchaseorder.location_id.id, context=context)
+                        cr, uid, purchaseorder._get_destination_location(), context=context)
                     if region_id:
                         exreg = region_mod.browse(cr, uid, region_id).code
             elif inv_line.invoice_id.type in ('out_invoice', 'out_refund'):