Fix process for cache management of browse record

When related records are created, the local cache of the browse record is not
clear so at the second loop in process the local cache is already filled with
empty one2many (like moves).

issue3111
review755002

sale.py

@@ -911,7 +911,8 @@ class Sale(Workflow, ModelSQL, ModelView):
     @Workflow.transition('processing')
     def process(self, ids):
         done = []
-        for sale in self.browse(ids):
+        for sale_id in ids:
+            sale = self.browse(sale_id)
             if sale.state in ('done', 'cancel'):
                 continue
             self.create_invoice(sale, 'out_invoice')