AddressHeader problem when FriendlyName is improperly quoted and contains comma

Bug report

Bug description:

Given an address text of the form: John Smith, Jr <johnsmith@example.com>
Because of the unquoted comma, the text is parsed as two addresses:
"John" <@smith>, "Jr" <johnsmith@example.com>
This is of greatest concern if the object is supposed to be a SingleAddressHeader.

I have also encountered TO and CC strings that have incomplete address specifications, containing only a Friendly Name. For these messages, I am only interested in the valid addresses, although others may want the existing behavior.

To work around both the parsing problem and the invalid address terms, I created a sub-class which discards any address where username or domain are not strings. My workaround does not correct for the incomplete Friendly Name, but it ensures a correct count of valid addresses. It would be desirable to implement a trap for unquoted commas, but there are so many challenges to parsing address lists correctly, I wonder if fixing the unquoted comma problem will create other headaches.

Problem observed on Python 3.11.3150.0 and Python 3.8.1

CPython versions tested on:

3.11

Operating systems tested on:

Windows

Iniziare dal comportamento di parsing di AddressHeader di CPython e riprodurre gli esempi relativi a una virgola non racchiusa tra virgolette e a un termine di indirizzo incompleto nelle versioni di Python indicate. Esaminare la discussione nei commenti prima di decidere la gestione prevista; il lavoro è completato quando è stato concordato un comportamento per le voci di indirizzo non valide o analizzate in modo ambiguo.