always set email for payment transaction

Closes #5519

facturier/views.py

@@ -152,8 +152,7 @@ class TransactionView(DetailView):
         # create an invoice :
         # 1. create a base from request and regie options
         invoice = {}
-        if hasattr(self.request.user, 'email'):
-            invoice['email'] = self.request.user.email
+        invoice['email'] = getattr(self.request.user, 'email', None)
         request_options = dict([(option.name, option.value) \
                                 for option in self.object.requestoption_set.all()])
         invoice.update(request_options)