MDEV-32259 Test from win.test fails with statement memory protection

The function setup_windows() called at the prepare phase of processing a
select builds a list of all window specifications used in the select. This list
is built on the statement memory and it must be done only once.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

sql/sql_lex.cc

@@ -2441,6 +2441,7 @@ void st_select_lex::init_query()
   m_custom_agg_func_used= false;
   window_specs.empty();
   window_funcs.empty();
+  is_win_spec_list_built= false;
   tvc= 0;
   in_tvc= false;
   versioned_tables= 0;

sql/sql_lex.h

@@ -1530,6 +1530,7 @@ class st_select_lex: public st_select_lex_node
                                        bool no_to_clones);
   
   List<Window_spec> window_specs;
+  bool is_win_spec_list_built;
   void prepare_add_window_spec(THD *thd);
   bool add_window_def(THD *thd, LEX_CSTRING *win_name, LEX_CSTRING *win_ref,
                       SQL_I_List<ORDER> win_partition_list,

sql/sql_window.cc

@@ -207,6 +207,9 @@ setup_windows(THD *thd, Ref_ptr_array ref_pointer_array, TABLE_LIST *tables,
   DBUG_ENTER("setup_windows");
   List_iterator<Window_spec> it(win_specs);
 
+  if (!thd->lex->current_select->is_win_spec_list_built)
+  {
+
     /*
       Move all unnamed specifications after the named ones.
       We could have avoided it if we had built two separate lists for
@@ -229,6 +232,9 @@ setup_windows(THD *thd, Ref_ptr_array ref_pointer_array, TABLE_LIST *tables,
 
     it.rewind();
 
+    thd->lex->current_select->is_win_spec_list_built= true;
+  }
+
   List_iterator_fast<Window_spec> itp(win_specs);
 
   while ((win_spec= it++))