Fix: Recognize ndns that put the headers into "message/global-headers" part (Improve ndn detection) (#2598)

I sent a message, and the ndn (Non Delivery Notification) was not parsed correctly, so here comes
the fix and the test.

test-data/message/testrun_ndn_2.eml

@@ -0,0 +1,97 @@
+Return-Path: <>
+Delivered-To: alice@example.org
+Received: from hq5.merlinux.eu
+	by hq5.merlinux.eu with LMTP
+	id IF/+LHrTFGEQBQAAPzvFDg
+	(envelope-from <>)
+	for <alice@example.org>; Thu, 12 Aug 2021 09:53:30 +0200
+Received: by hq5.merlinux.eu (Postfix)
+	id 9C87727A0006; Thu, 12 Aug 2021 09:53:30 +0200 (CEST)
+Date: Thu, 12 Aug 2021 09:53:30 +0200 (CEST)
+From: MAILER-DAEMON@hq5.merlinux.eu (Mail Delivery System)
+Subject: Undelivered Mail Returned to Sender
+To: alice@example.org
+Auto-Submitted: auto-replied
+MIME-Version: 1.0
+Content-Type: multipart/report; report-type=delivery-status;
+	boundary="A82D727A0003.1628754810/hq5.merlinux.eu"
+Content-Transfer-Encoding: 8bit
+Message-Id: <20210812075330.9C87727A0006@hq5.merlinux.eu>
+
+This is a MIME-encapsulated message.
+
+--A82D727A0003.1628754810/hq5.merlinux.eu
+Content-Description: Notification
+Content-Type: text/plain; charset=utf-8
+Content-Transfer-Encoding: 8bit
+
+This is the mail system at host hq5.merlinux.eu.
+
+I'm sorry to have to inform you that your message could not
+be delivered to one or more recipients. It's attached below.
+
+For further assistance, please send mail to postmaster.
+
+If you do so, please include this problem report. You can
+delete your own text from the attached returned message.
+
+                   The mail system
+
+<bob@example.org>: Host or domain name not found. Name service error for
+    name=echedelyr.tk type=AAAA: Host not found
+
+--A82D727A0003.1628754810/hq5.merlinux.eu
+Content-Description: Delivery report
+Content-Type: message/global-delivery-status
+Content-Transfer-Encoding: 8bit
+
+Reporting-MTA: dns; hq5.merlinux.eu
+X-Postfix-Queue-ID: A82D727A0003
+X-Postfix-Sender: rfc822; alice@example.org
+Arrival-Date: Thu, 12 Aug 2021 09:53:29 +0200 (CEST)
+
+Final-Recipient: rfc822; bob@example.org
+Original-Recipient: rfc822;bob@example.org
+Action: failed
+Status: 5.4.4
+Diagnostic-Code: X-Postfix; Host or domain name not found. Name service error
+    for name=echedelyr.tk type=AAAA: Host not found
+
+--A82D727A0003.1628754810/hq5.merlinux.eu
+Content-Description: Undelivered Message Headers
+Content-Type: message/global-headers
+Content-Transfer-Encoding: 8bit
+
+Return-Path: <alice@example.org>
+Chat-Disposition-Notification-To: alice@example.org
+DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=testrun.org;
+	s=testrun; t=1628754810;
+	bh=exDToKrRerWMZ62UQVK/RgNiwDDKe+GqF6zGdG64jl8=;
+	h=Subject:References:Date:To:From:From;
+	b=SNTTDdhkppXqimCSPP+cqDvdzmryYwzurtZdN2XkTVQEeqMMdnGvEA9TOgeZpHqi0
+	 oHSjJ5oD+eUK1ECnfRuxDF9DmFnK7sbw1MaHxIcAVTLPgHrMxv+2Fjq1nmrerzmr1t
+	 z9jOYY8e6gfEBw1uDAfHMmIl4OGuoDSll8haqNF3C2JqdwTtcdtE/w6ERJwSeHhCsR
+	 bknan9Rh75Tr46Zh8WVi9YYRVDGFj7+OlL/67Va+Jxl3c4v4EJ5vF6ncxyJupP9eU2
+	 qndV+g1BbxsARo663codYZRiGh217AI8DG2HUr0rVOPdvWm1kw/NTkp3BxoHkv5q2a
+	 Uak5Jiieur6Hg==
+Subject: Message from Hocuri
+Chat-User-Avatar: 0
+MIME-Version: 1.0
+References: <Mr.5xqflwt0YFv.IXDFfHauvWx@testrun.org>
+Date: Thu, 12 Aug 2021 07:53:28 +0000
+Chat-Version: 1.0
+Autocrypt: addr=alice@example.org;
+	keydata=xjMEX3tmZxYJKwYBBAHaRw8BAQdAl4LKVKPRqxG1ZXEO8e9s1DZWt6f38wSuJnY0mLSOuf
+	7NFTxob2N1cmkxQHRlc3RydW4ub3JnPsKLBBAWCAAzAhkBBQJfe2ZnAhsDBAsJCAcGFQgJCgsCAxYC
+	ARYhBBmltZLxgqC0SHJPEL7qvlxmQUTNAAoJEL7qvlxmQUTNIucBAJkRclHRG7cWpFbMYW+rspEFIQ
+	j1GTKwriiBpk5ffnroAQC3h/scScpG/EeIPL0y80GRS5BoR1Ium3zrlR92EaijDc44BF97ZmcSCisG
+	AQQBl1UBBQEBB0CmxhyX/NuXIlrl0/fdeEseAv6KCbZ4tV3tIvSvnH1KHgMBCAfCeAQYFggAIAUCX3
+	tmZwIbDBYhBBmltZLxgqC0SHJPEL7qvlxmQUTNAAoJEL7qvlxmQUTNnkYA/3qY+e6PrtR1WT7PiVeZ
+	RIQBkkJjWWSx+lBQ5fNb3e92AQCBEG3OnGy4RrxOqWW2ry7ETP33CJeiwAwCvv4LQlwCCw==
+Message-ID: <Mr.5xqflwt0YFv.IXDFfHauvWx@testrun.org>
+To: <bob@example.org>
+From: Hocuri <alice@example.org>
+Content-Type: multipart/mixed; boundary="qtFe0wPDNHWVlvqV0B8ymdWmE6ZmKD"
+
+--A82D727A0003.1628754810/hq5.merlinux.eu--
+