We should not call free_tmp_table() for derived table in 
mysql_derived_filling(), since by this moment this table is already
registered in THD::derived_tables list and thus free_tmp_table() will
be called for it automatically in close_thread_tables().


sql/sql_derived.cc:
  We should not call free_tmp_table() for derived table in 
  mysql_derived_filling(), since by this moment this table is already
  registered in THD::derived_tables list and thus free_tmp_table() will
  be called for it automatically in close_thread_tables().