sync_client errors out after 2.3.16 -> 2.5.9 upgrade

[Kenneth Marshall]

Hi Cyrus Developers,

Thank you for your patch to address the folder move problem between
un-reconstructed mailboxes after the 2.3.16 -> 2.5.9 upgrade. I am
not sure, but it looks like there may be another overly aggressive
check. I keep getting these fatal errors from sync_client:

Aug  1 16:24:16 cyrus1a imap/sync_client[14886]: SYNCERROR: guid mismatch user.robot 1696 (56412de8678bfb53f6cdb5fe4502031af5484056 0000000000000000000000000000000000000000)
Aug  1 16:24:16 cyrus1a imap/sync_client[14886]: SYNCERROR: guid mismatch user.robot 1697 (1b0024218a4419973b83ae3e84ac7133a4ab7d40 0000000000000000000000000000000000000000)
Aug  1 16:24:16 cyrus1a imap/sync_client[14886]: SYNCERROR: guid mismatch user.robot 1698 (f17084425d83bccb28a4dfa195846c7ef88c7567 0000000000000000000000000000000000000000)
Aug  1 16:24:16 cyrus1a imap/sync_client[14886]: SYNCERROR: guid mismatch user.robot 1699 (7a751e41e1d3a58e541298ab724be4c29d96e49d 0000000000000000000000000000000000000000)
Aug  1 16:24:16 cyrus1a imap/sync_client[14886]: SYNCERROR: guid mismatch user.robot 1700 (724a013d0ae97d27a1da33832487df1719681659 0000000000000000000000000000000000000000)
Aug  1 16:24:16 cyrus1a imap/sync_client[14886]: Fatal error: Internal error: assertion failed: imap/mailbox.c: 2850: !message_guid_isnull(&record->guid)

And then the sync_client has to be run manually and if lucky, it will
process the full log successfully. I was looking in imap/mailbox.c
and it looks like the assert at line 2850 may need a similar override
for non-upgraded folders:

-----------imap/mailbox.c---------------
/* append a single message to a mailbox - also updates everything
 * automatically.  These two functions are the ONLY way to modify
 * the contents or tracking fields of a message */
EXPORTED int mailbox_append_index_record(struct mailbox *mailbox,
                                struct index_record *record)
{
    indexbuffer_t ibuf;
    unsigned char *buf = ibuf.buf;
    size_t offset;
    int r;
    int n;
    struct utimbuf settime;
    uint32_t recno;

    assert(mailbox_index_islocked(mailbox, 1));

    /* Append MUST be a higher UID than any we've yet seen */
    assert(record->uid > mailbox->i.last_uid)

    /* Append MUST have a message with data */
    assert(record->size);

=====>    /* GUID must not be null */
=====>    assert(!message_guid_isnull(&record->guid));

    /* belt AND suspenders - check the previous record too */
    if (mailbox->i.num_records) {
        struct index_record prev;

-----------imap/mailbox.c---------------

What do you think?

Regards,
Ken