[FIX] purchase: keep fallback behaviour that was removed at rev 8973217e

If no valid invocie is found on the purchase order line, use the price and currency of the line (coherent with help message)

addons/purchase/stock.py

@@ -128,14 +128,23 @@ class stock_partial_picking(osv.osv_memory):
     # Overridden to inject the purchase price as true 'cost price' when processing
     # incoming pickings.
     def _product_cost_for_average_update(self, cr, uid, move):
-        if move.purchase_line_id and move.purchase_line_id and move.purchase_line_id.invoice_lines:
-            cost = move.price_unit
-            for inv_line in move.purchase_line_id.invoice_lines:
-                if inv_line.invoice_id.state not in ('draft', 'cancel'):
-                    inv_currency = inv_line.invoice_id.currency_id.id
-                    company_currency = inv_line.invoice_id.company_id.currency_id.id
-                    cost = self.pool.get('res.currency').compute(cr, uid, inv_currency, company_currency, inv_line.price_unit, round=False, context={'date': inv_line.invoice_id.date_invoice})
-                    return {'cost': cost, 'currency': company_currency}
+        purchase_line = move.purchase_line_id
+        if move.picking_id.purchase_id and purchase_line:
+            if any([x.invoice_id.state not in ('draft', 'cancel') for x in purchase_line.invoice_lines]):
+                # use price set on validated invoices
+                cost = move.price_unit
+                for inv_line in purchase_line.invoice_lines:
+                    if inv_line.invoice_id.state not in ('draft', 'cancel'):
+                        inv_currency = inv_line.invoice_id.currency_id.id
+                        company_currency = inv_line.invoice_id.company_id.currency_id.id
+                        cost = self.pool.get('res.currency').compute(cr, uid, inv_currency, company_currency, inv_line.price_unit, round=False, context={'date': inv_line.invoice_id.date_invoice})
+                        return {'cost': cost, 'currency': company_currency}
+            else:
+                # use price set on the purchase order
+                pur_currency = purchase_line.order_id.currency_id.id
+                company_currency = purchase_line.company_id.currency_id.id
+                cost = self.pool.get('res.currency').compute(cr, uid, pur_currency, company_currency, purchase_line.price_unit, round=False, context={'date': purchase_line.date_order})
+                return {'cost': cost, 'currency': company_currency}
         return super(stock_partial_picking, self)._product_cost_for_average_update(cr, uid, move)
 
     def __get_help_text(self, cursor, user, picking_id, context=None):