added validation-check for existing incorrect ibans

jdav_web/finance/models.py

@@ -516,9 +516,13 @@ class Transaction(models.Model):
         if self.amount == 0:
             return ""
 
-        reference = self.escape_reference(self.reference)
-        iban = IBAN(self.member.iban)
+        iban = IBAN(self.member.iban, allow_invalid=True)
+        if not iban.is_valid:
+            return ""
         bic = iban.bic
+
+        reference = self.escape_reference(self.reference)
+
         return f"""BCD
 001
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