order by

Problem was that the first index read was unordered,
and the next was ordered, resulting in use of
uninitialized data.

Solution was to use the correct variable to see if
the 'next' call should be ordered or not.

mysql-test/r/partition.result:
  Bug#40494: MYSQL server crashes on range access with
  partitioning and order by
  
  Added test case for the bug.
mysql-test/t/partition.test:
  Bug#40494: MYSQL server crashes on range access with
  partitioning and order by
  
  Added test case for the bug.
sql/ha_partition.cc:
  Bug#40494: MYSQL server crashes on range access with
  partitioning and order by
  
  Used the wrong variable to decide to continue with
  ordered or unordered scan.