commit cd857dd6 upstream.

We want to make sure the point is still within the extent item, not to verify
the memory it's pointing to.
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>