MDEV-23927 Crash in ./mtr --skip-innodb-fast-shutdown innodb.temporary_tables

innodb_preshutdown(): On innodb_fast_shutdown=0, only wait for
transactions to exit if the transaction system had been initialized.

Reviewed by: Vladislav Vaintroub

mysql-test/suite/innodb/t/temporary_table.test

@@ -131,7 +131,7 @@ AND support IN ('YES', 'DEFAULT', 'ENABLED');
 # We cannot use include/restart_mysqld.inc in this particular test,
 # because SHOW STATUS would fail due to unwritable (nonexistent) tmpdir.
 --source include/shutdown_mysqld.inc
---exec echo "restart: --tmpdir=/dev/null/nonexistent" > $_expect_file_name
+--exec echo "restart: --tmpdir=/dev/null/nonexistent --skip-innodb-fast-shutdown" > $_expect_file_name
 --enable_reconnect
 --disable_result_log
 --disable_query_log

storage/innobase/srv/srv0start.cc

@@ -2076,6 +2076,7 @@ void innodb_preshutdown()
     better prevent any further changes from being buffered. */
     innodb_change_buffering= 0;
 
+    if (trx_sys.is_initialised())
       while (trx_sys.any_active_transactions())
         os_thread_sleep(1000);
   }