IDL cache AVL tree initialize

servers/slapd/back-bdb/init.c

@@ -200,6 +200,7 @@ bdb_db_open( BackendDB *be )
 
 #ifdef SLAP_IDL_CACHE
 	if ( bdb->bi_idl_cache_max_size ) {
+		bdb->bi_idl_tree = NULL;
 		ldap_pvt_thread_rdwr_init( &bdb->bi_idl_tree_rwlock );
 		ldap_pvt_thread_mutex_init( &bdb->bi_idl_tree_lrulock );
 		bdb->bi_idl_cache_size = 0;