patch for ATAng bug

[Soren Schmidt]

It seems David Gilbert wrote:
> I submitted kern/56572 a few minutes ago.  It patches ata-disk.c to
> reject a disk that has zero blocks.
> 
> This is a good thing ... malicious or broken disks (compact flash,
> whatever) shouldn't crash machines.
> 
> But in this case, the detected ad3 doesn't exist.  The machine is a
> laptop with a drive on channel 0 and a DVD+R on channel 1.  If the DVD
> is removed, the phantom ad3 doesn't show up, either.
> 
> ... so that issue with ATAng is unresolved.

Uhm, I'm working on finding the real problem, and I'd like that to be
the solution. However the above may be a good workaround for those
bitten by this...

-Søren