Combine Clients; should not be able to combine Clients belonging to the same Account

When combining Clients you could select two clients that appear on the same Account. After the Clients have been combined the Account shows the same Client twice, and the Account cannot be saved until one of them is deleted.

This has been changed so the Client Combine wizard fails with the message "Failed to Refresh Clients to Combine. Both Clients cannot belong to the same Account '[AccountId]'.".