MDEV-24063 Assertion during graceful shutdown with wsrep_on=OFF

During graceful shutdowns, client connections are closed and
eventually and THD::awake() acquires LOCK_thd_data mutex which is
required later on in wsrep_thd_is_aborting(). Make sure LOCK_thd_data
is acquired, even if global wsrep_on is disabled.
Reviewed-by: Jan Lindström <jan.lindstrom@mariadb.com>

mysql-test/suite/galera/r/MDEV-24063.result

+connection node_2;
+connection node_1;
+connect node_2a, 127.0.0.1, root, , test, $NODE_MYPORT_2;
+connection node_2a;
+CREATE TABLE t1 (f1 INTEGER PRIMARY KEY);
+connection node_2;
+SET GLOBAL wsrep_on=OFF;
+DROP TABLE t1;

mysql-test/suite/galera/t/MDEV-24063.test

+#
+# MDEV-24063
+#
+# my_bool wsrep_thd_is_aborting(const THD*):
+# Assertion `((&(&thd->LOCK_thd_data)->m_mutex)->count > 0 &&
+# pthread_equal(pthread_self(), (&(&thd->LOCK_thd_data)->m_mutex)->thread))' failed.
+#
+
+--source include/galera_cluster.inc
+
+--connect node_2a, 127.0.0.1, root, , test, $NODE_MYPORT_2
+--connection node_2a
+CREATE TABLE t1 (f1 INTEGER PRIMARY KEY);
+
+--connection node_2
+SET GLOBAL wsrep_on=OFF;
+--source include/shutdown_mysqld.inc
+--source include/start_mysqld.inc
+
+DROP TABLE t1;

sql/sql_class.h

@@ -3308,7 +3308,7 @@ class THD: public THD_count, /* this must be first */
   void awake_no_mutex(killed_state state_to_set);
   void awake(killed_state state_to_set)
   {
-    bool wsrep_on_local= WSREP_NNULL(this);
+    bool wsrep_on_local= variables.wsrep_on;
     /*
       mutex locking order (LOCK_thd_data - LOCK_thd_kill)) requires
       to grab LOCK_thd_data here