Possibly incorrect test when checking for (name, email) tuple

https://github.com/lavr/python-emails/blob/eb1adb459116bcc66b7e413a468e1a97336034d9/emails/utils.py#LL134C69-L134C70

I think this test might be incorrect? Perhaps the line should read as follows:

```py
if isinstance(e, string_types) and (not n or isinstance(n, string_types)):
```