scsi: don't trust the data we receive from the drive too

  much. It very well might have errors (like zero response length).
  Seen on Megaraid logical drive, and verified in the driver source.


git-svn-id: https://smartmontools.svn.sourceforge.net/svnroot/smartmontools/trunk@297 4ea69e1a-61f1-4043-bf83-b5c94c648137