[gnome-control-center] display: prevent a crash if the screen being dragged is removed

[Thomas Wood <thos src gnome org>]

commit 0a938e815d5c988f8abf023663de9d12b9ba4d58
Author: Thomas Wood <thomas wood intel com>
Date:   Wed Jul 17 11:05:11 2013 +0100

    display: prevent a crash if the screen being dragged is removed
    
    https://bugzilla.gnome.org/show_bug.cgi?id=704389

 panels/display/cc-display-panel.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)
---
diff --git a/panels/display/cc-display-panel.c b/panels/display/cc-display-panel.c
index 02cf94d..1db8f47 100644
--- a/panels/display/cc-display-panel.c
+++ b/panels/display/cc-display-panel.c
@@ -1742,6 +1742,13 @@ set_primary_output (CcDisplayPanel *self,
 }
 
 static void
+grab_weak_ref_notify (gpointer  area,
+                      GObject  *object)
+{
+  foo_scroll_area_end_grab (area, NULL);
+}
+
+static void
 on_output_event (FooScrollArea *area,
                  FooScrollAreaEvent *event,
                  gpointer data)
@@ -1783,6 +1790,7 @@ on_output_event (FooScrollArea *area,
          gnome_rr_output_info_get_geometry (output, &output_x, &output_y, NULL, NULL);
 
          foo_scroll_area_begin_grab (area, on_output_event, data);
+         g_object_weak_ref (data, grab_weak_ref_notify, area);
 
          info = g_new0 (GrabInfo, 1);
          info->grab_x = event->x;
@@ -1855,6 +1863,7 @@ on_output_event (FooScrollArea *area,
 
              g_free (g_object_get_data (G_OBJECT (output), "grab-info"));
              g_object_set_data (G_OBJECT (output), "grab-info", NULL);
+             g_object_weak_unref (data, grab_weak_ref_notify, area);
 
 #if 0
               g_debug ("new position: %d %d %d %d", output->x, output->y, output->width, output->height);