streamline test

test-data/message/attach_filename_combined.eml

@@ -0,0 +1,31 @@
+Subject: Test combined filenames
+Message-ID: 12345@testrun.org
+Date: Sat, 07 Dec 2019 19:00:27 +0000
+X-Mailer: Kopano 8.7.16
+To: recp@testrun.org
+From: sender@testrun.org
+Content-Type: multipart/mixed; boundary="NwkNRwaJw1M5n2xcr2ODfAqvTjcj9Z"
+
+
+--NwkNRwaJw1M5n2xcr2ODfAqvTjcj9Z
+Content-Type: text/plain; charset=utf-8
+
+yip, filename may be given twice,
+seen this way in Kopano.
+
+normally, both filenames will be the same,
+for the test, we use different filenames,
+we define that `filename` has a higher precedence.
+
+-- 
+Sent with my Delta Chat Messenger: https://delta.chat
+
+--NwkNRwaJw1M5n2xcr2ODfAqvTjcj9Z
+Content-Type: text/html
+Content-Disposition: attachment; filename="=?utf-8?Q?Ma=C3=9Fnahmen_Okt=2E_2020=2Ehtml?=";
+ filename*=utf-8''Ma%C3%9Fnahmen%20Okt.%202020.ignored.html
+Content-Transfer-Encoding: base64
+
+PGh0bWw+PGJvZHk+dGV4dDwvYm9keT5kYXRh
+
+--NwkNRwaJw1M5n2xcr2ODfAqvTjcj9Z--