[FIX] point_of_sale: error picking

- Create a stockable and a service product
- In the POS, sell 1 unit of the stockable product and -1 unit of the
  service product
- Validate and pay

2 pickings are created: a picking containing the stockable product which
stays in state 'Draft' and an empty picking in state 'Available'.

The problem comes from the negative quantity on a service product: we
should filter out services when checking the quantities.

opw-745712

addons/point_of_sale/point_of_sale.py

@@ -1042,10 +1042,10 @@ class pos_order(osv.osv):
                     'location_id': location_id,
                     'location_dest_id': destination_id,
                 }
-                pos_qty = any([x.qty > 0 for x in order.lines])
+                pos_qty = any([x.qty > 0 for x in order.lines if x.product_id.type in ['product', 'consu']])
                 if pos_qty:
                     order_picking_id = picking_obj.create(cr, uid, picking_vals.copy(), context=context)
-                neg_qty = any([x.qty < 0 for x in order.lines])
+                neg_qty = any([x.qty < 0 for x in order.lines if x.product_id.type in ['product', 'consu']])
                 if neg_qty:
                     return_vals = picking_vals.copy()
                     return_vals.update({