wio-lib.pl: Fixes bug#13040 - Change multipart/mixed to multipart/alternative
- Thunderbird and Roundcube mail clients presume that any mail with Content Type of
multipart/mixed has an attachment included rather than actually checking for
disposition attachment. This means that any mail with multipart/mixed gets the
attachment icon marked up even though there is no attachment.
- Although this is a problem of the clients involved, in this case the simplest solution
is to change multipart/mixed to multipart/alternative as WIO Mail only sends text
without any attachment or other part to indicate that a client is active or inactive.
- Confirmed on my vm testbed
Fixes: Bug#13040 Tested-by: Adolf Belka <adolf.belka@ipfire.org> Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>