Save correct number of a visitor's messages for threads related to of…

…fline messages

src/mibew/libs/classes/Mibew/RequestProcessor/ThreadProcessor.php

@@ -795,6 +795,7 @@ protected function apiProcessLeaveMessage($args)
         $thread->userId = $visitor['id'];
         $thread->userAgent = $user_browser;
         $thread->state = Thread::STATE_LEFT;
+        $thread->messageCount = 1;
         $thread->closed = time();
         $thread->save();