may return a wrong result.

An Item_sum_hybrid object has the was_values flag which indicates whether any
values were added to the sum function. By default it is set to true and reset
to false on any no_rows_in_result() call. This method is called only in
return_zero_rows() function. An ALL/ANY subquery can be optimized by MIN/MAX
optimization. The was_values flag is used to indicate whether the subquery
has returned at least one row. This bug occurs because return_zero_rows() is
called only when we know that the select will return zero rows before
starting any scans but often such information is not known.
In the reported case the return_zero_rows() function is not called and
the was_values flag is not reset to false and yet the subquery return no rows
Item_func_not_all and Item_func_nop_all functions return a wrong
comparison result.

The end_send_group() function now calls no_rows_in_result() for each item
in the fields_list if there is no rows were found for the (sub)query.


mysql-test/t/subselect.test:
  Added test case for bug#18503: Queries with a quantified subquery returning empty set may return a wrong result.
mysql-test/r/subselect.result:
  Added test case for bug#18503: Queries with a quantified subquery returning empty set may return a wrong result.
sql/sql_select.cc:
  Fixed bug#18503: Queries with a quantified subquery returning empty set may return a wrong result.
  
  The end_send_group() function now calls no_rows_in_result() for each item
  in the fields_list if there is no matching rows were found.