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

@@ -207,27 +207,33 @@ setup_windows(THD *thd, Ref_ptr_array ref_pointer_array, TABLE_LIST *tables,
   DBUG_ENTER("setup_windows");
   List_iterator<Window_spec> it(win_specs);
 
-  /* 
-    Move all unnamed specifications after the named ones.
-    We could have avoided it if we had built two separate lists for
-    named and unnamed specifications.
-  */
-  Query_arena *arena, backup;
-  arena= thd->activate_stmt_arena_if_needed(&backup);
-  uint i = 0;
-  uint elems= win_specs.elements;
-  while ((win_spec= it++) && i++ < elems)
+  if (!thd->lex->current_select->is_win_spec_list_built)
   {
-    if (win_spec->name() == NULL)
+
+    /*
+      Move all unnamed specifications after the named ones.
+      We could have avoided it if we had built two separate lists for
+      named and unnamed specifications.
+    */
+    Query_arena *arena, backup;
+    arena= thd->activate_stmt_arena_if_needed(&backup);
+    uint i = 0;
+    uint elems= win_specs.elements;
+    while ((win_spec= it++) && i++ < elems)
     {
-      it.remove();
-      win_specs.push_back(win_spec);
+      if (win_spec->name() == NULL)
+      {
+        it.remove();
+        win_specs.push_back(win_spec);
+      }
     }
-  }
-  if (arena)
-    thd->restore_active_arena(arena, &backup);
+    if (arena)
+      thd->restore_active_arena(arena, &backup);
 
-  it.rewind();
+    it.rewind();
+
+    thd->lex->current_select->is_win_spec_list_built= true;
+  }
 
   List_iterator_fast<Window_spec> itp(win_specs);