qxl-render: fix broken vnc+spice since commit f934493

Notify any listeners such as vnc that the displaysurface has been
changed, otherwise they will segfault when first accessing the freed old
displaysurface data.
Signed-off-by: NAlon Levy <alevy@redhat.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/qxl-render.c

@@ -127,6 +127,7 @@ static void qxl_render_update_area_unlocked(PCIQXLDevice *qxl)
                     qxl->guest_primary.surface.width,
                     qxl->guest_primary.surface.height);
         }
+        dpy_resize(vga->ds);
     }
     for (i = 0; i < qxl->num_dirty_rects; i++) {
         if (qemu_spice_rect_is_empty(qxl->dirty+i)) {