The crash happens because original join table is replaced with temporary table
at execution stage and later we attempt to use this temporary table in
select_describe. It might happen that
Item_subselect::update_used_tables() method which sets const_item flag
is not called by some reasons (no where/having conditon in subquery for example).
It prevents JOIN::join_tmp creation and breaks original join.
The fix is to call ::update_used_tables() before ::const_item() check.


mysql-test/r/ps.result:
  test case
mysql-test/t/ps.test:
  test case
sql/item_subselect.cc:
  call ::update_used_tables() before ::const_item() check.