Fix long delay when attempting to transfer a file that is in-use on the remote system

To recreate:

Open a file on the remote system

Select the file on the remote system, Ctrl+C

Switch back to your local desktop, Ctrl+V

What happens: The file transfer progress dialog displays and hangs for a minute with no progress before failing.

What we'd like to have happen: Immediately, an error message appears that indicates that the file is in use.

This request originated in a ticket - see Service Ticket#8283903 for the exchange.