Modified the test case for patch of the bug #12144
  to display status of Handler_read_next before and
  after the tested query.


mysql-test/r/null_key.result:
  Modified the test case for patch of the bug #12144
  to display status of Handler_read_next before and
  after the tested query.
mysql-test/t/null_key.test:
  Modified the test case for patch of the bug #12144
  to display status of Handler_read_next before and
  after the tested query.