It is possible to delete message from the receiver's inbox

When the sender deletes his PM before the reciever reads it, the reciever's message counter displays that a message was recieved even though there is no message in the Inbox folder.

Preconditions: User1 and User2 are created, both users have Send_Messages permission.

Steps to reproduce:
1. Log in as User1
2. Go to the Messages page
3. Compose and send message to the User2
4. Delete this message from the Outbox folder
5. Log out
6. Log in as User2
Note, that Message counter value is (1)
7. Go to the Inbox folder

Actual result: There is no message from User1 in the folder
Expected result: Message counter displays (1 and message is shown);