vhost-user-gpu: do not send scanout update if no GPU socket

Should fix coverity CID 1401760.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20190605145829.7674-2-marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

contrib/vhost-user-gpu/main.c

@@ -354,7 +354,7 @@ vg_disable_scanout(VuGpu *g, int scanout_id)
     scanout->width = 0;
     scanout->height = 0;
 
-    {
+    if (g->sock_fd >= 0) {
         VhostUserGpuMsg msg = {
             .request = VHOST_USER_GPU_SCANOUT,
             .size = sizeof(VhostUserGpuScanout),