[FIX] purchase: Wrong scheduled date for backorder

Fine tuning of this commit:7333f5e

When the PO lines were not ordered according to the scheduled date,
the scheduled date of the picking was wrong when delivering.

opw:752192

addons/purchase/purchase.py

@@ -358,7 +358,7 @@ class PurchaseOrder(models.Model):
                 moves = order.order_line.filtered(lambda r: r.product_id.type in ['product', 'consu'])._create_stock_moves(picking)
                 move_ids = moves.action_confirm()
                 seq = 0
-                for move in moves:
+                for move in sorted(moves, key=lambda move: move.date_expected):
                     seq += 5
                     move.sequence = seq
                 moves = self.env['stock.move'].browse(move_ids)