MDEV-21563 FTS thread aborts during shutdown

- Added the test case in innodb_fts suite
- Updated copyright year in row0mysql.cc

mysql-test/suite/innodb_fts/r/misc_debug2.result

+call mtr.add_suppression("InnoDB: Table '.*' tablespace is set as discarded.");
+CREATE TABLE mdev21563(f1 VARCHAR(100), FULLTEXT idx(f1))ENGINE=InnoDB;
+set debug_dbug="+d,fts_instrument_sync_request";
+INSERT INTO mdev21563 VALUES('This is a test');
+ALTER TABLE mdev21563 DISCARD TABLESPACE;
+DROP TABLE mdev21563;

mysql-test/suite/innodb_fts/t/misc_debug2.test

+--source include/have_innodb.inc
+--source include/have_debug.inc
+--source include/not_embedded.inc
+call mtr.add_suppression("InnoDB: Table '.*' tablespace is set as discarded.");
+
+CREATE TABLE mdev21563(f1 VARCHAR(100), FULLTEXT idx(f1))ENGINE=InnoDB;
+set debug_dbug="+d,fts_instrument_sync_request";
+INSERT INTO mdev21563 VALUES('This is a test');
+ALTER TABLE mdev21563 DISCARD TABLESPACE;
+--source include/restart_mysqld.inc
+DROP TABLE mdev21563;

storage/innobase/row/row0mysql.cc

 /*****************************************************************************
 
 Copyright (c) 2000, 2018, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2015, 2019, MariaDB Corporation.
+Copyright (c) 2015, 2020, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software

storage/xtradb/row/row0mysql.cc

 /*****************************************************************************
 
 Copyright (c) 2000, 2018, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2015, 2019, MariaDB Corporation.
+Copyright (c) 2015, 2020, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software