MDEV-25457 Server crashes in row_undo_mod_clust_low upon rollback of read-only transaction

node->index was NULL.
But it's possible to get dict_table_t* from another source.

mysql-test/suite/innodb/r/temporary_table.result

@@ -754,3 +754,8 @@ COUNT(*)
 INSERT INTO t VALUES (0);
 SET SESSION tx_read_only=OFF;
 DROP TABLE t;
+CREATE TEMPORARY TABLE t (a INT) ENGINE=InnoDB;
+INSERT INTO t VALUES (1);
+START TRANSACTION READ ONLY;
+UPDATE t SET a = NULL;
+ROLLBACK;

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

@@ -595,3 +595,9 @@ SELECT COUNT(*)FROM t;
 INSERT INTO t VALUES (0);
 SET SESSION tx_read_only=OFF;
 DROP TABLE t;
+
+CREATE TEMPORARY TABLE t (a INT) ENGINE=InnoDB;
+INSERT INTO t VALUES (1);
+START TRANSACTION READ ONLY;
+UPDATE t SET a = NULL;
+ROLLBACK;

storage/innobase/row/row0umod.cc

@@ -109,7 +109,8 @@ row_undo_mod_clust_low(
 	ut_ad(success);
 	ut_ad(rec_get_trx_id(btr_cur_get_rec(btr_cur),
 			     btr_cur_get_index(btr_cur))
-	      == thr_get_trx(thr)->id || node->index->table->is_temporary());
+	      == thr_get_trx(thr)->id
+	      || btr_cur_get_index(btr_cur)->table->is_temporary());
 
 	if (mode != BTR_MODIFY_LEAF
 	    && dict_index_is_online_ddl(btr_cur_get_index(btr_cur))) {