segfault in ctl_mboxlist -d with 2.5.4

[Chris Stromsoe]

I'm seeing a segfault running ctl_mboxlist -d with 2.5.4.  mailboxes.db 
format is twoskip.  All mailbxoes are on the default partition.

gdb traces it back to this printf() in dump_cb():
    case DUMP:
        if (!d->partition || !strcmpsafe(d->partition, part)) {
            printf("%s\t%d %s %s\n", name, mbtype, part, acl);
            if (d->purge) {
                cyrusdb_delete(mbdb, key, keylen, &(d->tid), 0);
            }
        }
        break;


Initializing part to NULL at the start of the function fixes the segfault.

The mailbox causing the problem has MBTYPE_DELETED.  Tracing through the 
logic earlier in dump_cb(), the call to dlist_getatom() is failing but the 
partition is not being set to NULL because the if explicitly excludes 
mailboxes of MBTYPE_DELETED.

            // The partition is always there...
            r = dlist_getatom(dl, "P", (const char **)&part);

            if (!r && !(mbtype & MBTYPE_DELETED)) {
                syslog(
                        LOG_ERR,
                        "No partition for mailbox '%s'",
                        name
                    );

                part = NULL;
            }

The test should probably be rewritten to be:

            if (!r) {
                if (!(mbtype & MBTYPE_DELETED)) {
                    syslog(
                            LOG_ERR,
                            "No partition for mailbox '%s'",
                            name
                        );
                }
                part = NULL;
            }



-Chris