SIGSEGV in ft_boolean_check_syntax_string on setting ft_boolean_syntax

# mysqld options required for replay: --character-set-server=utf16

SET GLOBAL ft_boolean_syntax=' ~/!@#$%^&*()-';

Core was generated by `/test/MD200720-mariadb-10.5.5-linux-x86_64-dbg/bin/mysqld --no-defaults --core-'.

Program terminated with signal SIGSEGV, Segmentation fault.

#0  __pthread_kill (threadid=<optimized out>, signo=signo@entry=11)

    at ../sysdeps/unix/sysv/linux/pthread_kill.c:57

[Current thread is 1 (Thread 0x14bb72bec700 (LWP 1762217))]

(gdb) bt

#0  __pthread_kill (threadid=<optimized out>, signo=signo@entry=11) at ../sysdeps/unix/sysv/linux/pthread_kill.c:57

#1  0x000055f87fa7182d in my_write_core (sig=sig@entry=11) at /test/10.5_dbg/mysys/stacktrace.c:518

#2  0x000055f87f22b75c in handle_fatal_signal (sig=11) at /test/10.5_dbg/sql/signal_handler.cc:330

#3  <signal handler called>

#4  0x000055f87f9ff71d in ft_boolean_check_syntax_string (str=<optimized out>) at /test/10.5_dbg/storage/myisam/ft_parser.c:93

#5  0x000055f87f0eb83c in check_ftb_syntax (self=<optimized out>, thd=<optimized out>, var=<optimized out>) at /test/10.5_dbg/sql/sys_vars.cc:1183

#6  0x000055f87ee97150 in sys_var::check (this=0x55f8807eaac0 <Sys_ft_boolean_syntax>, thd=thd@entry=0x14bb4f015088, var=var@entry=0x14bb4f074398) at /test/10.5_dbg/sql/set_var.cc:246

#7  0x000055f87ee981e0 in set_var::check (this=0x14bb4f074398, thd=0x14bb4f015088) at /test/10.5_dbg/sql/set_var.cc:811

#8  0x000055f87ee9890c in sql_set_variables (thd=thd@entry=0x14bb4f015088, var_list=var_list@entry=0x14bb4f019fb0, free=free@entry=true) at /test/10.5_dbg/sql/set_var.cc:739

#9  0x000055f87ef81b8f in mysql_execute_command (thd=thd@entry=0x14bb4f015088) at /test/10.5_dbg/sql/sql_parse.cc:5008

#10 0x000055f87ef8bb8a in mysql_parse (thd=thd@entry=0x14bb4f015088, rawbuf=<optimized out>, length=<optimized out>, parser_state=parser_state@entry=0x14bb72beb350, is_com_multi=is_com_multi@entry=false, is_next_command=is_next_command@entry=false) at /test/10.5_dbg/sql/sql_parse.cc:7993

#11 0x000055f87ef7863c in dispatch_command (command=command@entry=COM_QUERY, thd=thd@entry=0x14bb4f015088, packet=packet@entry=0x14bb4f067089 "SET GLOBAL ft_boolean_syntax=' ~/!@#$%^&*()-'", packet_length=packet_length@entry=45, is_com_multi=is_com_multi@entry=false, is_next_command=is_next_command@entry=false) at /test/10.5_dbg/sql/sql_parse.cc:1866

#12 0x000055f87ef76e16 in do_command (thd=0x14bb4f015088) at /test/10.5_dbg/sql/sql_parse.cc:1347

#13 0x000055f87f0d34af in do_handle_one_connection (connect=<optimized out>, connect@entry=0x14bb51cc9808, put_in_cache=put_in_cache@entry=true) at /test/10.5_dbg/sql/sql_connect.cc:1411

#14 0x000055f87f0d3bcb in handle_one_connection (arg=arg@entry=0x14bb51cc9808) at /test/10.5_dbg/sql/sql_connect.cc:1313

#15 0x000055f87f537dca in pfs_spawn_thread (arg=0x14bb6f846508) at /test/10.5_dbg/storage/perfschema/pfs.cc:2201

#16 0x000014bb71b656db in start_thread (arg=0x14bb72bec700) at pthread_create.c:463

#17 0x000014bb70f63a3f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95