[FIX] stock: traceback package tree view

_compute_package_info iterate on package but
sometimes self is used resulting in an ensure one
exception.

addons/stock/models/stock_quant.py

@@ -330,8 +330,8 @@ class QuantPackage(models.Model):
     def _compute_package_info(self):
         for package in self:
             values = {'location_id': False, 'company_id': self.env.user.company_id.id, 'owner_id': False}
-            if self.quant_ids:
-                values['location_id'] = self.quant_ids[0].location_id
+            if package.quant_ids:
+                values['location_id'] = package.quant_ids[0].location_id
             package.location_id = values['location_id']
             package.company_id = values['company_id']
             package.owner_id = values['owner_id']