bug#53716: 29.0.50; Failure to parse addresses with angle-brackets without display names

[Michael Welsh Duggan]

Attempting to send an email to an address like <foo@example.com> without
an attached display name causes the address to be flagged as suspicious.

Recipe from emacs -Q:

    C-x m
    <foo@example.com>
    C-n Test
    C-c C-c

This results in Emacs notifying me that there is a suspicious address.

According to RFC 5322, an address can be a mailbox, which can be a
name-addr, which is an optional display-name followed by an angle-addr.
So an address like

    <foo@example.com>

without an attached display name should be parsed as a valid address.
The problem appears to be caused by a bug in `ietf-drums-parse-address'.
Near the end of the function it calls `rfc2047-decode-string' on the
current `display-string', which is, at this point, `nil'.


In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version 
1.16.0)
 of 2022-01-31 built on miko
Repository revision: cce477cad7ffffbfc1a21e9dd711b32f8e2b3ea3
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
System Description: Debian GNU/Linux bookworm/sid

Configured using:
 'configure --without-toolkit-scroll-bars --with-x-toolkit=lucid
 --with-native-compilation --with-xinput2'

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG JSON
LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NATIVE_COMP
NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF X11
XAW3D XDBE XIM XINPUT2 XPM LUCID ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Message

Features:
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dynamic-setting system-font-setting font-render-setting cairo x-toolkit
xinput2 x multi-tty make-network-process native-compile emacs)

-- 
Michael Welsh Duggan
(md5i@md5i.com)