patch for ATAng bug

[David Gilbert]

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.

Dave.

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|David Gilbert, Independent Contractor.       | Two things can only be     |
|Mail:       dave at daveg.ca                    |  equal if and only if they |
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