Fix purchase_compute_order error when a product is no more available for a supplier

intercoop_addons/purchase_compute_order/model/product_product.py

@@ -22,6 +22,9 @@
 ##############################################################################
 
 from openerp import models, api, fields
+import logging
+
+_logger = logging.getLogger(__name__)
 
 
 class ProductProduct(models.Model):
@@ -56,5 +59,9 @@ class ProductProduct(models.Model):
         if not self.product_tmpl_id.seller_ids:
             return False
         valid_si = self._all_valid_psi()[0]
-        seq = min([si.sequence for si in valid_si])
-        return valid_si.filtered(lambda si, seq=seq: si.sequence == seq)
+	if len(valid_si) > 0:
+            seq = min([si.sequence for si in valid_si])
+            return valid_si.filtered(lambda si, seq=seq: si.sequence == seq)
+	else:
+            _logger.warning("No fisrt_valid_psi %s", str(self.product_tmpl_id))
+            return False