[3.11] gh-118643: Fix AttributeError in the email module (GH-119099) (#119393)

Fix regression introduced in gh-100884: AttributeError when re-fold a long
address list.

Also fix more cases of incorrect encoding of the address separator in the
address list missed in gh-100884.
(cherry picked from commit 858b9e85fcdd495947c9e892ce6e3734652c48f2)