single row subquery always can return NULL (no rows found) (BUG#5590)


mysql-test/r/subselect.result:
  maybe_null flag returning by subquwery for temporary table creation
mysql-test/t/subselect.test:
  maybe_null flag returning by subquwery for temporary table creation
sql/item.cc:
  storing maybe_null in type holder
sql/item_subselect.cc:
  single row subquery always can return NULL (no rows found)
sql/sql_derived.cc:
  fixed error handling if creating derived table failed