Closing the SB when a DC file transfer is running, causes wrong UI updates.

[valerio]

When a Direct Connection is going on, WLM can still close the chat's switchboard at random.

KMess receives the BYE command and notifies the user interface that the transfer has failed: both the Transfer Window and the chat are updated with "Transfer Failed" messages.

But the DC is still running in background, and when it eventually finishes or fails, the UI is updated again with the appropriate message. But only the chat window receives the update: the Transfer Window still says "transfer failed" even if the transfer had succeeded.