Add extra mutex check to wsrep_aborting_thd_enqueue

sql/wsrep_mysqld.cc

@@ -2739,6 +2739,7 @@ my_bool wsrep_aborting_thd_contains(THD *thd)
 
 void wsrep_aborting_thd_enqueue(THD *thd)
 {
+  mysql_mutex_assert_owner(&LOCK_wsrep_rollback);
   wsrep_aborting_thd_t aborting = (wsrep_aborting_thd_t)
           my_malloc(sizeof(struct wsrep_aborting_thd), MYF(0));
   aborting->aborting_thd  = thd;