[at-spi2-core] Fix an invalid free introduced in 2.39.90, along with some warnings

[Mike Gorse <mgorse src gnome org>]

commit 40e972450fc5ce928914a380e32b33129033d4da
Author: Mike Gorse <mgorse suse com>
Date:   Mon Feb 22 12:31:15 2021 -0600

    Fix an invalid free introduced in 2.39.90, along with some warnings
    
            Fixes https://gitlab.gnome.org/GNOME/at-spi2-core/issues/30

 atspi/atspi-accessible.c     | 2 +-
 atspi/atspi-event-listener.c | 5 +++--
 atspi/atspi-misc.c           | 7 +++----
 3 files changed, 7 insertions(+), 7 deletions(-)
---
diff --git a/atspi/atspi-accessible.c b/atspi/atspi-accessible.c
index 58d7316f..b078688c 100644
--- a/atspi/atspi-accessible.c
+++ b/atspi/atspi-accessible.c
@@ -418,7 +418,7 @@ atspi_accessible_get_parent (AtspiAccessible *obj, GError **error)
     }
     dbus_message_iter_init (reply, &iter);
     dbus_message_iter_recurse (&iter, &iter_variant);
-    g_object_unref (obj->accessible_parent);
+    g_clear_object (&obj->accessible_parent);
     obj->accessible_parent = _atspi_dbus_return_accessible_from_iter (&iter_variant);
     dbus_message_unref (reply);
     _atspi_accessible_add_cache (obj, ATSPI_CACHE_PARENT);
diff --git a/atspi/atspi-event-listener.c b/atspi/atspi-event-listener.c
index 00957dd1..ca6828fe 100644
--- a/atspi/atspi-event-listener.c
+++ b/atspi/atspi-event-listener.c
@@ -864,7 +864,8 @@ atspi_event_copy (AtspiEvent *src)
   dst->detail2 = src->detail2;
   g_value_init (&dst->any_data, G_VALUE_TYPE (&src->any_data));
   g_value_copy (&src->any_data, &dst->any_data);
-  dst->sender = g_object_ref (src->sender);
+  if (src->sender)
+    dst->sender = g_object_ref (src->sender);
   return dst;
 }
 
@@ -874,7 +875,7 @@ atspi_event_free (AtspiEvent *event)
   g_object_unref (event->source);
   g_free (event->type);
   g_value_unset (&event->any_data);
-  g_object_unref (event->sender);
+  g_clear_object (&event->sender);
   g_free (event);
 }
 
diff --git a/atspi/atspi-misc.c b/atspi/atspi-misc.c
index f897c7ea..7af46e9f 100644
--- a/atspi/atspi-misc.c
+++ b/atspi/atspi-misc.c
@@ -465,7 +465,8 @@ add_accessible_from_iter (DBusMessageIter *iter)
       else
       {
         /* This place is already taken - let's free this place with dignity */
-        g_object_unref (g_ptr_array_index (accessible->accessible_parent->children, index));
+        if (g_ptr_array_index (accessible->accessible_parent->children, index))
+          g_object_unref (g_ptr_array_index (accessible->accessible_parent->children, index));
       }
       g_ptr_array_index (accessible->accessible_parent->children, index) = g_object_ref (accessible);
     }
@@ -1273,7 +1274,7 @@ _atspi_dbus_get_property (gpointer obj, const char *interface, const char *name,
   process_deferred_messages ();
   if (!reply)
   {
-    // TODO: throw exception
+    /* TODO: throw exception */
     goto done;
   }
 
@@ -1300,14 +1301,12 @@ _atspi_dbus_get_property (gpointer obj, const char *interface, const char *name,
   }
   if (!strcmp (type, "(so)"))
   {
-    g_object_unref (*(AtspiAccessible**)data);
     *((AtspiAccessible **)data) = _atspi_dbus_return_accessible_from_iter (&iter_variant);
   }
   else
   {
     if (type [0] == 's')
     {
-      g_free (*(char**)data);
       *(char**) data = NULL;
     }