ui/gtk: gd_draw_event returns FALSE when no cairo surface is bound

gd_draw_event shouldn't try to repaint if surface does not exist
for the VC.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
Message-Id: <20211104065153.28897-4-dongwon.kim@intel.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

ui/gtk.c

@@ -778,6 +778,9 @@ static gboolean gd_draw_event(GtkWidget *widget, cairo_t *cr, void *opaque)
     if (!vc->gfx.ds) {
         return FALSE;
     }
+    if (!vc->gfx.surface) {
+        return FALSE;
+    }
 
     vc->gfx.dcl.update_interval =
         gd_monitor_update_interval(vc->window ? vc->window : s->window);