The view sets the message before populateMessageBody() fills its
attachments, so attachments() is still empty when the plugin looks for
the calendar part, and it never looked again: the event panel did not
show up for most invitations. Subscribe to msg.attachments until the
part is found or another message is shown, and drop a late result that
belongs to a message no longer displayed.
The panel never appears on a real invitation.
msg.attachments is a ko.observableArray, so msg.attachments.find() is
undefined and throws inside the message subscription - the rest of the
handler, including the JSON-LD path, dies with it. The app itself always
writes attachments().
A scheduling mail also does not necessarily carry a text/calendar
attachment. Evolution and Exchange put the scheduling part inline in
multipart/alternative as text/calendar and repeat it as an
application/ics attachment, so such a message shows two .ics files and
the current test matches neither reliably. Match text/calendar,
application/ics, text/x-vcalendar or an .ics file name - which is what
the commented-out line above was reaching for.
