This patch updates the seqNums after an Expunge operation. When an
expunge operation occurs, the seqNum of the deleted message is reported.
The Imap spec [0] states that an immediate decrement of all seqnums greater
than the deleted occurs, even before the next reporting of an expunge
update.
[0]: https://datatracker.ietf.org/doc/html/rfc3501#section-7.4.1
Fixes: https://todo.sr.ht/~rjarry/aerc/61
Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
Signed-off-by: Robin Jarry <robin@jarry.cc>