parallels: Sanity check for s->tracks (CVE-2014-0142) This avoids a possible division by zero. Convert s->tracks to unsigned as well because it feels better than surviving just because the results of calculations with s->tracks are converted to unsigned anyway. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>