MDEV-25766 Unused CTE lead to a crash in find_field_in_tables/find_order_in_list

Do not assume that subquery Item always present.

mysql-test/r/cte_nonrecursive.result

@@ -2184,4 +2184,37 @@ select * from t1;
 a
 7
 drop table t1,t2;
+#
+# MDEV-25766: Unused CTE lead to a crash in
+# find_field_in_tables/find_order_in_list
+#
+create table t1 (f1 INTEGER);
+create view v1 as
+select
+subq_0.c4 as c2,
+subq_0.c4 as c4
+from
+(select
+ref_0.f1 as c4
+from
+t1 as ref_0
+where (select 1)
+) as subq_0
+order by c2, c4 desc;
+WITH
+unused_with AS (select
+subq_0.c4 as c6
+from
+(select
+11 as c4
+from
+v1 as ref_0
+) as subq_0,
+v1 as ref_2
+)
+select 1 ;
+1
+1
+drop view v1;
+drop table t1;
 # End of 10.2 tests

mysql-test/t/cte_nonrecursive.test

@@ -1624,4 +1624,40 @@ select * from t1;
 
 drop table t1,t2;
 
+--echo #
+--echo # MDEV-25766: Unused CTE lead to a crash in
+--echo # find_field_in_tables/find_order_in_list
+--echo #
+
+create table t1 (f1 INTEGER);
+
+create view v1 as
+select
+    subq_0.c4 as c2,
+    subq_0.c4 as c4
+  from
+    (select
+          ref_0.f1 as c4
+        from
+          t1 as ref_0
+        where (select 1)
+        ) as subq_0
+  order by c2, c4 desc;
+
+WITH
+unused_with AS (select
+    subq_0.c4 as c6
+  from
+    (select
+            11 as c4
+          from
+            v1 as ref_0
+     ) as subq_0,
+     v1 as ref_2
+)
+select 1 ;
+
+drop view v1;
+drop table t1;
+
 --echo # End of 10.2 tests

sql/sql_base.cc

@@ -6011,9 +6011,10 @@ find_field_in_tables(THD *thd, Item_ident *item,
              sl=sl->outer_select())
         {
           Item *subs= sl->master_unit()->item;
-          if (subs->type() == Item::SUBSELECT_ITEM && 
-              ((Item_subselect*)subs)->substype() == Item_subselect::IN_SUBS &&
-              ((Item_in_subselect*)subs)->test_strategy(SUBS_SEMI_JOIN))
+          if (!subs ||
+              (subs->type() == Item::SUBSELECT_ITEM &&
+               ((Item_subselect*)subs)->substype() == Item_subselect::IN_SUBS &&
+               ((Item_in_subselect*)subs)->test_strategy(SUBS_SEMI_JOIN)))
           {
             continue;
           }