Backport from 5.2: Fix valgrind failure: Don't access item_func->arguments()

if item_func->argument_count()==0

sql/sql_show.cc

@@ -1909,11 +1909,9 @@ bool uses_only_table_name_fields(Item *item, TABLE_LIST *table)
   if (item->type() == Item::FUNC_ITEM)
   {
     Item_func *item_func= (Item_func*)item;
-    Item **child;
-    Item **item_end= (item_func->arguments()) + item_func->argument_count();
-    for (child= item_func->arguments(); child != item_end; child++)
+    for (uint i=0; i<item_func->argument_count(); i++)
     {
-      if (!uses_only_table_name_fields(*child, table))
+      if (!uses_only_table_name_fields(item_func->arguments()[i], table))
         return 0;
     }
   }