virtio-gpu: update scanout if there is any area covered by the rect

The scanout is currently updated only if the whole rect is inside the
scanout space. This is not a correct condition because the scanout should
be updated even a small area in the scanout space is covered by the rect.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20220909014052.7297-1-dongwon.kim@intel.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>