SIGSEGV in ha_spider::lock_tables on BEGIN after table lock

INSTALL PLUGIN Spider SONAME 'ha_spider.so';

CREATE USER Spider@localhost IDENTIFIED BY '';

CREATE SERVER srv FOREIGN DATA WRAPPER MYSQL OPTIONS (SOCKET '../socket.sock',DATABASE 'test',user 'Spider',PASSWORD '');

CREATE TABLE t (c INT) ENGINE=InnoDB;

CREATE TABLE t1 (c INT) ENGINE=Spider COMMENT='WRAPPER "mysql",srv "srv",TABLE "t"';

SELECT * FROM t1;

LOCK TABLES t1 WRITE CONCURRENT,t1 AS t2 READ;

BEGIN;

Core was generated by `/test/MD221022-mariadb-10.11.1-linux-x86_64-opt/bin/mysqld --no-defaults --core'.

Program terminated with signal SIGSEGV, Segmentation fault.

#0  0x0000152d3d82cd4e in ha_spider::lock_tables (

    this=this@entry=0x152ccc04bb50)

    at /test/10.11_opt/storage/spider/ha_spider.cc:12184

12184	        if (

[Current thread is 1 (Thread 0x152d3d8d6700 (LWP 354245))]

(gdb) bt

#0  0x0000152d3d82cd4e in ha_spider::lock_tables (this=this@entry=0x152ccc04bb50) at /test/10.11_opt/storage/spider/ha_spider.cc:12184

#1  0x0000152d3d82d200 in ha_spider::external_lock (this=0x152ccc04bb50, thd=<optimized out>, lock_type=2) at /test/10.11_opt/storage/spider/ha_spider.cc:921

#2  0x000055aa825b5d78 in handler::ha_external_lock (this=0x152ccc04bb50, thd=thd@entry=0x152ccc000c58, lock_type=lock_type@entry=2) at /test/10.11_opt/sql/handler.cc:7095

#3  0x000055aa826cb55c in handler::ha_external_unlock (thd=0x152ccc000c58, this=<optimized out>) at /test/10.11_opt/sql/handler.h:3538

#4  unlock_external (count=<optimized out>, table=0x152ccc0813f8, thd=0x152ccc000c58) at /test/10.11_opt/sql/lock.cc:744

#5  mysql_unlock_tables (thd=0x152ccc000c58, sql_lock=0x152ccc0813b8, free_lock=<optimized out>) at /test/10.11_opt/sql/lock.cc:435

#6  0x000055aa826cbad8 in mysql_unlock_tables (thd=thd@entry=0x152ccc000c58, sql_lock=<optimized out>) at /test/10.11_opt/sql/lock.cc:418

#7  0x000055aa822f2209 in close_thread_tables (thd=thd@entry=0x152ccc000c58) at /test/10.11_opt/sql/sql_base.cc:953

#8  0x000055aa822f307b in Locked_tables_list::unlock_locked_tables (thd=0x152ccc000c58, this=0x152ccc004af8) at /test/10.11_opt/sql/sql_base.cc:2571

#9  Locked_tables_list::unlock_locked_tables (this=this@entry=0x152ccc004af8, thd=thd@entry=0x152ccc000c58) at /test/10.11_opt/sql/sql_base.cc:2542

#10 0x000055aa8248f28d in trans_begin (thd=thd@entry=0x152ccc000c58, flags=0) at /test/10.11_opt/sql/transaction.cc:115

#11 0x000055aa8236a1ae in mysql_execute_command (thd=0x152ccc000c58, is_called_from_prepared_stmt=<optimized out>) at /test/10.11_opt/sql/sql_parse.cc:5605

#12 0x000055aa82358335 in mysql_parse (rawbuf=<optimized out>, length=<optimized out>, parser_state=<optimized out>, thd=0x152ccc000c58) at /test/10.11_opt/sql/sql_parse.cc:8023

#13 mysql_parse (thd=0x152ccc000c58, rawbuf=<optimized out>, length=<optimized out>, parser_state=<optimized out>) at /test/10.11_opt/sql/sql_parse.cc:7945

#14 0x000055aa823640ea in dispatch_command (command=COM_QUERY, thd=0x152ccc000c58, packet=<optimized out>, packet_length=<optimized out>, blocking=<optimized out>) at /test/10.11_opt/sql/sql_class.h:1346

#15 0x000055aa82365ee2 in do_command (thd=0x152ccc000c58, blocking=blocking@entry=true) at /test/10.11_opt/sql/sql_parse.cc:1407

#16 0x000055aa8247ffbf in do_handle_one_connection (connect=<optimized out>, connect@entry=0x55aa8599ac18, put_in_cache=put_in_cache@entry=true) at /test/10.11_opt/sql/sql_connect.cc:1416

#17 0x000055aa8248029d in handle_one_connection (arg=0x55aa8599ac18) at /test/10.11_opt/sql/sql_connect.cc:1318

#18 0x0000152d63b56609 in start_thread (arg=<optimized out>) at pthread_create.c:477

#19 0x0000152d63742133 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95