Backport MDEV-19848 (Server crashes in check_vcol_forward_refs upon INSERT DELAYED into table with long blob key)

CREATE  TABLE t1 (a BLOB, UNIQUE(a)) ENGINE=MyISAM;

INSERT DELAYED t1 () VALUES ();

# Cleanup

DROP TABLE t1;

#3  <signal handler called>

#4  0x000055b5f6a33e95 in check_vcol_forward_refs (field=field@entry=0x7fea4c012318, vcol=<optimized out>, check_constraint=check_constraint@entry=false) at /data/src/10.4/sql/table.cc:3471

#5  0x000055b5f6a3b475 in parse_vcol_defs (thd=thd@entry=0x7fea4c0009a8, mem_root=0x7fea4c006188, table=table@entry=0x7fea4c0113d0, error_reported=error_reported@entry=0x7fea5d28c350, mode=mode@entry=VCOL_INIT_DEPENDENCY_FAILURE_IS_WARNING) at /data/src/10.4/sql/table.cc:1284

#6  0x000055b5f695ebb2 in Delayed_insert::get_local_table (this=this@entry=0x7fea4c0d1008, client_thd=client_thd@entry=0x7fea4c0009a8) at /data/src/10.4/sql/sql_insert.cc:2651

#7  0x000055b5f6962a12 in delayed_get_table (grl_protection_request=0x7fea5d28c530, table_list=<optimized out>, thd=0x55b5f7a9baa0 <LOCK_delayed_insert>) at /data/src/10.4/sql/sql_insert.cc:2481

#8  open_and_lock_for_insert_delayed (table_list=<optimized out>, thd=0x55b5f7a9baa0 <LOCK_delayed_insert>) at /data/src/10.4/sql/sql_insert.cc:573

#9  mysql_insert (thd=thd@entry=0x7fea4c0009a8, table_list=<optimized out>, fields=..., values_list=..., update_fields=..., update_values=..., duplic=<optimized out>, ignore=<optimized out>) at /data/src/10.4/sql/sql_insert.cc:759

#10 0x000055b5f699004a in mysql_execute_command (thd=thd@entry=0x7fea4c0009a8) at /data/src/10.4/sql/sql_parse.cc:4528

#11 0x000055b5f6994c69 in mysql_parse (thd=thd@entry=0x7fea4c0009a8, rawbuf=<optimized out>, length=30, parser_state=parser_state@entry=0x7fea5d28e5b0, is_com_multi=is_com_multi@entry=false, is_next_command=is_next_command@entry=false) at /data/src/10.4/sql/sql_parse.cc:7900

#12 0x000055b5f6996e5f in dispatch_command (command=command@entry=COM_QUERY, thd=thd@entry=0x7fea4c0009a8, packet=packet@entry=0x7fea4c007a19 "INSERT DELAYED t1 () VALUES ()", packet_length=packet_length@entry=30, is_com_multi=is_com_multi@entry=false, is_next_command=is_next_command@entry=false) at /data/src/10.4/sql/sql_parse.cc:1842

#13 0x000055b5f69985d1 in do_command (thd=0x7fea4c0009a8) at /data/src/10.4/sql/sql_parse.cc:1360

#14 0x000055b5f6a67e04 in do_handle_one_connection (connect=connect@entry=0x55b5f8f89fe8) at /data/src/10.4/sql/sql_connect.cc:1412

#15 0x000055b5f6a67eb4 in handle_one_connection (arg=arg@entry=0x55b5f8f89fe8) at /data/src/10.4/sql/sql_connect.cc:1316

#16 0x000055b5f700aec4 in pfs_spawn_thread (arg=0x55b5f8f02f38) at /data/src/10.4/storage/perfschema/pfs.cc:1869

#17 0x00007fea6506f4a4 in start_thread (arg=0x7fea5d28f700) at pthread_create.c:456

#18 0x00007fea631a3d0f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:97