[FIX] sale: hide update_prices button correctly

Steps:
 - Active Pricelist
 - Create SO --> add some lines
 - Change Pricelist and remove lines

Issue:
- Button to Update prices is still visible

Fix:
- Button should not be visible as there are no lines

closes odoo/odoo#73038

X-original-commit: aab38f9d52f8629eaea1a3725e4909ac5df1b067
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>

addons/sale/models/sale_order.py

@@ -471,7 +471,7 @@ class SaleOrder(models.Model):
                 }
             }
 
-    @api.onchange('pricelist_id')
+    @api.onchange('pricelist_id', 'order_line')
     def _onchange_pricelist_id(self):
         if self.order_line and self.pricelist_id and self._origin.pricelist_id != self.pricelist_id:
             self.show_update_pricelist = True