Write errors on FAT fs

Follow these steps after booting JNode to reproduce the buggy behaviour:
- execute the commands
cd jnode
touch test
edit test
- type some text into the file then save it. This is the first time you save the file created with touch and it works. After exitting the the editor 'cat test' will show the contents of the file correctly.
- edit the file again with: edit test
- make same changes and save it
- at this point you get an exception that you can see in the attachment (the stacktrace should be visible in the console after exitting the editor)
- after this point on subsequent attempts of saving the file a FileNotFoundException is reported.
You can still open and read the file with the editor but when you try to save it the file is not found. I think this is an illegal use of the FileNotFoundException in the underlying code.