In registration_data_export_interface(), the object_path is obtained using:

object_path = g_dbus_object_get_object_path (G_DBUS_OBJECT (data->object));

But when exporting an object uniquely, the object_path is not assigned
to the GDBusObject until after all the interfaces are exported.
Therefore, registration_data_export_interface() is trying to export
the interface on the non-unique object path, which can lead to
run-time errors if an object already exists on that path.

Instead, registration_data_export_interface() should be passed the
object_path explicitly, as is done in
g_dbus_object_manager_server_export_unlocked().

Signed-off-by: David Zeuthen <davidz@redhat.com>