MDEV-10669: Crash in SELECT with window function used

Make sure to call split_sum_func on all items that contain window
functions, so that all the column references are set up correctly.

mysql-test/r/win.result

@@ -2211,3 +2211,28 @@ a	b	simple_sum	sum_and_const	sum_and_sum
 3.0000000000	2	5.5000000000	6.5000000000	11.5000000000
 4.5000000000	2	10.0000000000	11.0000000000	18.0000000000
 drop table t;
+#
+# MDEV-10669: Crash in SELECT with window function used
+#
+create table t(a decimal(35,10), b int);
+insert into t(a,b) values(1,1);
+insert into t(a,b) values(2,1);
+insert into t(a,b) values(0,1);
+SELECT (CASE WHEN sum(t.a) over (partition by t.b)=0 THEN null ELSE null END) AS a FROM t;
+a
+NULL
+NULL
+NULL
+SELECT ifnull(((t.a) / CASE WHEN sum(t.a) over(partition by t.b) =0 then null else null end) ,0) from t;
+ifnull(((t.a) / CASE WHEN sum(t.a) over(partition by t.b) =0 then null else null end) ,0)
+0.00000000000000
+0.00000000000000
+0.00000000000000
+SELECT sum(t.a) over (partition by t.b order by a),
+sqrt(ifnull((sum(t.a) over (partition by t.b order by a)), 0))
+from t;
+sum(t.a) over (partition by t.b order by a)	sqrt(ifnull((sum(t.a) over (partition by t.b order by a)), 0))
+1.0000000000	1
+3.0000000000	1.7320508075688772
+0.0000000000	0
+drop table t;

mysql-test/t/win.test

@@ -1357,3 +1357,17 @@ select a, b,
 from t
 order by t.b, t.a;
 drop table t;
+
+--echo #
+--echo # MDEV-10669: Crash in SELECT with window function used
+--echo #
+create table t(a decimal(35,10), b int);
+insert into t(a,b) values(1,1);
+insert into t(a,b) values(2,1);
+insert into t(a,b) values(0,1);
+SELECT (CASE WHEN sum(t.a) over (partition by t.b)=0 THEN null ELSE null END) AS a FROM t;
+SELECT ifnull(((t.a) / CASE WHEN sum(t.a) over(partition by t.b) =0 then null else null end) ,0) from t;
+SELECT sum(t.a) over (partition by t.b order by a),
+       sqrt(ifnull((sum(t.a) over (partition by t.b order by a)), 0))
+from t;
+drop table t;

sql/item.cc

@@ -1870,7 +1870,7 @@ void Item::split_sum_func2(THD *thd, Ref_ptr_array ref_pointer_array,
         ((Item_sum *) this)->ref_by)
       return;
   }
-  else if (type() == WINDOW_FUNC_ITEM)
+  else if (type() == WINDOW_FUNC_ITEM || with_window_func)
   {
     /*
       Skip the else part, window functions are very special functions: