[FIX] sale_stock: product_id_change_with_wh

When changing the quantity of a SO line, the product_id_change_with_wh
must be triggered to check the availability of this product.

opw:668236

addons/sale_stock/sale_stock_view.xml

@@ -57,7 +57,7 @@
                         False, parent.warehouse_id, context)
                       </attribute>
                     </xpath>
-                    <xpath expr="//field[@name='order_line']/form//field[@name='product_uom_qty']" position="attributes">
+                    <xpath expr="//field[@name='order_line']/tree//field[@name='product_uom_qty']" position="attributes">
                       <attribute name="on_change">product_id_change_with_wh(
                         parent.pricelist_id, product_id, product_uom_qty, product_uom, product_uos_qty, False, name, 
                         parent.partner_id, False, False, parent.date_order, product_packaging, parent.fiscal_position,