`◆?` charcter appears in the subject when it has multiple MIME lines

Describe the bug

Graphical character (◆ + ?) appears in the subject of some mails written in Japanese language.

To Reproduce

Post a mail with subject like:

Subject: =?ISO-2022-JP?B?GyRCRnxLXDhsJEhGfEtcOGwkSEZ8S1w4bCROJUElJyVDGyhC?=
 =?ISO-2022-JP?B?GyRCJS8bKEI=?=

Current K-9 shows 日本語と日本語と日本語のチェッ◆ク on both tray list mode and mail content mode.

Expected behavior Though the example subject has a newline, this should be parsed as one-line ‘日本語と日本語と日本語のチェック’ by MIME decoding rule for subject. It looks current K-9 simply trys to show (unexpected) newline char.

Screenshots Tray mode

Content mode has same problem also

Environment (please complete the following information):

• K-9 Mail version: 5.904
• Android version: 12
• Device: Google Pixel 6
• Account type: IMAP

Additional context It seems same as #3622. I’m not sure what was done by ‘Fixed in master’. (Because I hadn’t used K-9 mail since 2019, I didn’t know it was fixed at that time.)

[kmuto]

I confirmed this issue was fixed in v5.905. Thank you! 😄

[cketti]

Thunderbird ran into the same problem: https://bugzilla.mozilla.org/show_bug.cgi?id=1374149

I’m adopting their fix for K-9 Mail.