update: Don't release the thread object from this precise thread.

This is not safe and not supported.

src/misc/update.c

@@ -1079,6 +1079,7 @@ void update_Delete( update_t *p_update )
     {
         vlc_object_kill( p_update->p_download );
         vlc_thread_join( p_update->p_download );
+        vlc_object_release( p_update->p_download );
     }
 
     vlc_mutex_destroy( &p_update->lock );
@@ -1682,9 +1683,6 @@ end:
     free( p_buffer );
     free( psz_size );
 
-    p_udt->p_update->p_download = NULL;
-
-    vlc_object_release( p_udt );
     return NULL;
 }