If we have a non-empty file and the version doesn't match, then we truncate and
write our own version. If the file is empty we write our version and the
truncate becomes a no-op
Signed-off-by: Christian Decker <decker.christian@gmail.com>
As proposed by @rustyrussell this makes it a bit easier to truncate and sync on
read errors.
Signed-off-by: Christian Decker <decker.christian@gmail.com>