the wrong buffer
Post-pushbuild fix
Added test case for better coverage.


mysql-test/r/partition.result:
  Bug#22351 - handler::index_next_same() call to key_cmp_if_same() uses
              the wrong buffer
  Added test result
mysql-test/t/partition.test:
  Bug#22351 - handler::index_next_same() call to key_cmp_if_same() uses
              the wrong buffer
  Added test case