sortlength: Conditional jump or move depends on uninitialised value

$ perl ./mtr type_inet.type_inet6 --valgrind

type_inet.type_inet6                     [ fail ]  Found warnings/errors in server log file!

        Test ended at 2020-04-14 22:40:39

line

==22724== Thread 6:

==22724== Conditional jump or move depends on uninitialised value(s)

==22724==    at 0xD19FD2: sortlength(THD*, Sort_keys*, bool*, bool*) (filesort.cc:2269)

==22724==    by 0xD139DF: filesort(THD*, TABLE*, Filesort*, Filesort_tracker*, JOIN*, unsigned long long) (filesort.cc:252)

==22724==    by 0xA49543: create_sort_index(THD*, JOIN*, st_join_table*, Filesort*) (sql_select.cc:23860)

==22724==    by 0xA43523: st_join_table::sort_table() (sql_select.cc:21589)

==22724==    by 0xA430FA: join_init_read_record(st_join_table*) (sql_select.cc:21528)

==22724==    by 0xA40E8C: sub_select(JOIN*, st_join_table*, bool) (sql_select.cc:20602)

==22724==    by 0xA40343: do_select(JOIN*, Procedure*) (sql_select.cc:20139)

==22724==    by 0xA13F0D: JOIN::exec_inner() (sql_select.cc:4463)

==22724==    by 0xA13036: JOIN::exec() (sql_select.cc:4244)

==22724==    by 0xA14769: mysql_select(THD*, TABLE_LIST*, List<Item>&, Item*, unsigned int, st_order*, st_order*, Item*, st_order*, unsigned long long, select_result*, st_select_lex_unit*, st_select_lex*) (sql_select.cc:4668)

==22724==    by 0xA040DF: handle_select(THD*, LEX*, select_result*, unsigned long) (sql_select.cc:429)

==22724==    by 0x9C8833: execute_sqlcom_select(THD*, TABLE_LIST*) (sql_parse.cc:6168)

==22724==    by 0x9BF2B9: mysql_execute_command(THD*) (sql_parse.cc:3901)

==22724==    by 0x9CD83D: mysql_parse(THD*, char*, unsigned int, Parser_state*, bool, bool) (sql_parse.cc:7953)

==22724==    by 0x9B8F40: dispatch_command(enum_server_command, THD*, char*, unsigned int, bool, bool) (sql_parse.cc:1840)

==22724==    by 0x9B7676: do_command(THD*) (sql_parse.cc:1359)

==22724==    by 0xB61B36: do_handle_one_connection(CONNECT*, bool) (sql_connect.cc:1422)

==22724==    by 0xB61865: handle_one_connection (sql_connect.cc:1319)

==22724==    by 0x10B30F9: pfs_spawn_thread (pfs.cc:2201)

==22724==    by 0x4E3F4A3: start_thread (pthread_create.c:456)

^ Found warnings in /dev/shm/var_valgrind/log/mysqld.1.err