[at-spi2-core] Fix crash with event listener deregistration

[Mike Gorse <mgorse src gnome org>]

commit e76171adce37b073aeaf0f96379ff99c450c8a5d
Author: Mike Gorse <mgorse novell com>
Date:   Wed Dec 29 03:57:29 2010 -0500

    Fix crash with event listener deregistration

 atspi/atspi-event-listener.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/atspi/atspi-event-listener.c b/atspi/atspi-event-listener.c
index 438cb78..aa78562 100644
--- a/atspi/atspi-event-listener.c
+++ b/atspi/atspi-event-listener.c
@@ -534,7 +534,8 @@ atspi_event_listener_register_from_callback (AtspiEventListenerCB callback,
     return;
   dbus_message_append_args (message, DBUS_TYPE_STRING, &event_type, DBUS_TYPE_INVALID);
   reply = _atspi_dbus_send_with_reply_and_block (message);
-  dbus_message_unref (reply);
+  if (reply)
+    dbus_message_unref (reply);
 
   return TRUE;
 }
@@ -627,9 +628,13 @@ atspi_event_listener_deregister_from_callback (AtspiEventListenerCB callback,
         is_superset (name, e->name) &&
         is_superset (detail, e->detail))
     {
+      gboolean need_replace;
       DBusError error;
       DBusMessage *message, *reply;
+      need_replace = (l == event_listeners);
       l = g_list_remove (l, e);
+      if (need_replace)
+        event_listeners = l;
       dbus_error_init (&error);
       dbus_bus_remove_match (_atspi_bus(), matchrule, &error);
       dbus_error_init (&error);