The index (key_part_1, key_part-2) was erroneously considered as compatible
with the required ordering in the function test_test_if_order_by_key when 
a query with an ORDER BY clause contained a condition of the form
  key_part_1=const OR key_part_1 IS NULL 
and the order list contained only key_part_2. This happened because the value
of the const_key_parts field in the KEYUSE structure was not formed correctly
for the keys that could be used for ref_or_null access. 
This was fixed in the code of the update_ref_and_keys function.
The problem could not manifest itself for MyISAM databases because the
implementation of the keys_to_use_for_scanning() handler function always
returns an empty bitmap for the MyISAM engine.


mysql-test/r/innodb_mysql.result:
  Added a test case for bug #32815.
mysql-test/t/innodb_mysql.test:
  Added a test case for bug #32815.
sql/sql_select.cc:
  Fixed bug #32815.
  The index (key_part_1, key_part-2) was erroneously considered as compatible
  with the required ordering in the function test_test_if_order_by_key when 
  a query with an ORDER BY clause contained a condition of the form
    key_part_1=const OR key_part_1 IS NULL 
  and the order list contained only key_part_2. This happened because the value
  of the const_key_parts field in the KEYUSE structure was not formed correctly
  for the keys that could be used for ref_or_null access. 
  This was fixed in the code of the update_ref_and_keys function.