Damn, the dirty rectangle values are signed integers. So the checks
added by commit 788fbf042fc6d5aaeab56757e6dad622ac5f0c21 are not good
enough, we also have to make sure they are not negative.
[ Note: There must be something broken in spice-server so we get
negative values in the first place. Bug opened:
https://bugzilla.redhat.com/show_bug.cgi?id=1135372 ]
Cc: qemu-stable@nongnu.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>