Check if usb or sd has enough free space before dump

[briantho]

Hi, I would like to make a suggestion for an enhancement. It would be nice if wudump could check free space before dumping, (right after pressing a for sd and b for usb) and if there is less than 23.3gb of free space on the device, just give an error message. This would be useful so you wouldn't need to keep checking free of a usb device, on a computer, and so wudump won't freeze if it runs out of space. Should be fairly simple to implement.
Thanks