Prevent transfer to MCU unless MCU name field is filled in

When the MCU Name textbox is blank and you click Transfer, the app freezes on "Saving files". One of the ways MCU name would be blank is if you control-click the selected file on the left file list.
The only I have been able to recover from this is to end-task via Task Manager (Windows).

Thanks for report, I'll reproduce and fix this in next few days.