Messages counter is shown incorrectly in case user was offline when it arrives

Steps to reproduce:
1. Create and activate User1 and User2
2. User1 is online, User2 offline.
Send 1 message from User1 to User2.
3. Logout User1.
4. Sign In as User2.
Overview the Messages counter; Messages(0) is shown instead of Messages(1)
5. Go to Inbox. Click on new message to read it and overview the messages counter.
Messages(-1) is shown instead of Messages(0)

P.S. This functionality works correctly in case message arrive when user is logged in (regardless if forum opened or not)