check that session codes are unique

When a new support session is created from the ScreenConnect web UI, it auto-generates a random four number session code for the client to connect, however at present no checking is done to see if the newly created session code is unique across all existing sessions. If the session code already exist the customer is connected to the existing session rather than the new session. This is extremely confusing as there is no way to determine which session the customer has connected to and indeed why they have not connected to the session you have just created for them! In my opinion this is a bug however when I reported it as such I was told this was by design - very poor design in my humble opinion!