ATA-ACS-3 says "If the two byte range length is zero, then the LBA
Range Entry shall be discarded as padding." iovecs are used as if
they are linearized, so it is incorrect to discard the rest of
this iovec.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>