[gnome-boxes] Fix regression when going back from properties

[Alexander Larsson <alexl src gnome org>]

commit cccd53118d91dc2de76f3a6c7a2fe0c2453ba200
Author: Alexander Larsson <alexl redhat com>
Date:   Mon Nov 5 11:23:31 2012 +0100

    Fix regression when going back from properties
    
    We accidentally destroyed the spice display widget in
    steal_display_widget_from_thumbnail(). We need to remove it
    before destroying the actor.

 src/machine.vala |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/src/machine.vala b/src/machine.vala
index c06b7c9..490fddd 100644
--- a/src/machine.vala
+++ b/src/machine.vala
@@ -572,8 +572,10 @@ private class Boxes.MachineActor: Boxes.UI {
 
     private Widget? steal_display_widget_from_thumbnail () {
         Widget? widget = null;
-        if (thumbnail is GtkClutter.Actor)
+        if (thumbnail is GtkClutter.Actor) {
             widget = (thumbnail as GtkClutter.Actor).contents;
+            (thumbnail as GtkClutter.Actor).contents = null;
+        }
         thumbnail.destroy ();
         thumbnail = null;
         thumbnail_screenshot = null;