dbus: fix the CanSetFullscreen property getter

Make org.mpris.MediaPlayer2.CanSetFullscreen true only when
a vout thread is running.

modules/control/dbus/dbus_root.c

@@ -101,7 +101,18 @@ DBUS_METHOD( Identity )
 static int
 MarshalCanSetFullscreen( intf_thread_t *p_intf, DBusMessageIter *container )
 {
-    const dbus_bool_t b_ret = (p_intf->p_sys->p_playlist) ? TRUE : FALSE;
+    input_thread_t *p_input = NULL;
+    dbus_bool_t     b_ret   = FALSE;
+
+    if (p_intf->p_sys->p_input)
+    {
+        p_input = (input_thread_t*) vlc_object_hold( p_intf->p_sys->p_input );
+        vout_thread_t* p_vout = input_GetVout( p_input );
+        vlc_object_release( p_input );
+
+        if ( p_vout )
+            b_ret = TRUE;
+    }
 
     dbus_message_iter_append_basic( container, DBUS_TYPE_BOOLEAN, &b_ret );
     return VLC_SUCCESS;