improve Item_field::register_field_in_read_map()

make it to work when read_set == vcol_set, that is, when
the caller wants to get a one complete bitmap of all fields
a particular vcol depends on.

sql/item.cc

@@ -901,17 +901,15 @@ bool Item_field::find_item_in_field_list_processor(void *arg)
 bool Item_field::register_field_in_read_map(void *arg)
 {
   TABLE *table= (TABLE *) arg;
-  if (field->table == table || !table)
-    bitmap_set_bit(field->table->read_set, field->field_index);
+  int res= 0;
   if (field->vcol_info &&
-      !bitmap_is_set(field->table->vcol_set, field->field_index))
+      !bitmap_fast_test_and_set(field->table->vcol_set, field->field_index))
   {
-    /* Ensure that the virtual fields is updated on read or write */
-    bitmap_set_bit(field->table->vcol_set, field->field_index);
-    return field->vcol_info->expr_item->walk(&Item::register_field_in_read_map,
-                                             1, arg);
+    res= field->vcol_info->expr_item->walk(&Item::register_field_in_read_map,1,arg);
   }
-  return 0;
+  if (field->table == table || !table)
+    bitmap_set_bit(field->table->read_set, field->field_index);
+  return res;
 }
 
 /*