IMAP: ignore extra ENABLED CONDSTORE QRESYNC responses when syncing a mailbox

Apparently at least some versions of Kolab are happy to send out unsolicited
ENABLED responses during the SELECT processing despite the fact that the QRESYNC
has been already enabled explicitly. This is in violation of my understanding of
RFC 5161. Reported to Kolab at https://issues.kolab.org/show_bug.cgi?id=2708 .

Thanks to Martin Sandsmark <martin.sandsmark@kde.org> for reporting this and
patiently providing logs until I was sure where the problem is. Much
appreciated!

BUG: 329204
REVIEW: 114666