Updated Win32WindowDemo.java

That demo does not work on my machine. So I tried to fixed it. Works on my machine now for detecting: add/remove CD, add/remove removeable hard drive.
I changed the parent window to null, because it doesn't work with device change, but I don't know why. I tested: the other function of this demo (onMachineLocked/onMachineUnlocked) can still work after my changing.