xfs_scrub: tread zero-length read verify as an IO error

xfs_scrub: tread zero-length read verify as an IO error

While doing some chaos testing on the xfs_scrub read verify code, I
noticed that if the device under a live filesystem gets resized while
scrub is running a media scan, reads will start returning 0.  This
causes read_verify() to run around in an infinite loop instead of
erroring out like it should.

Cc: <linux-xfs@vger.kernel.org> # v5.3.0
Fixes: 27464242956fac ("xfs_scrub: fix read verify disk error handling strategy")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>