Fix sync loop if all messages in a folder were filtered on initial sync

We are only calling $folder->setChanges() if we found changes for a folder.
If all messages are older than our filter window, we never called setChanges().
Therefore the total message count was still zero.

The next time we ping() the folder, the total message count
does not match for the folder -> we have a positive "ping".
This results in a sync loop.

Since we simplified the CONDSTORE / non-CONDSTORE handling,
there is no need to store "total_messages" in a separate variable.
Just get it from the saved IMAP state which we update unconditionally.

Bug: 12606 - Fix regression caused by addition of message count check in imap pinging.

Signed-off-by: Michael J Rubinsky <mrubinsk@horde.org>