Prevent superusers when they make a transaction with a non-member user

apps/note/models/transactions.py

@@ -202,7 +202,8 @@ class Transaction(PolymorphicModel):
         When saving, also transfer money between two notes
         """
         with transaction.atomic():
-            self.refresh_from_db()
+            if self.pk:
+                self.refresh_from_db()
             self.source.refresh_from_db()
             self.destination.refresh_from_db()
             self.validate(False)