[FIX] mrp: mrp_production.delivery_count more robust

when no group_id on mrp_production, set the delivery_count to 0

closes odoo/odoo#35372

Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>

addons/mrp/models/mrp_production.py

@@ -179,7 +179,7 @@ class MrpProduction(models.Model):
     def _compute_picking_ids(self):
         for order in self:
             order.picking_ids = self.env['stock.picking'].search([
-                ('group_id', '=', order.procurement_group_id.id),
+                ('group_id', '=', order.procurement_group_id.id), ('group_id', '!=', False),
             ])
             order.delivery_count = len(order.picking_ids)