Needed some special handling of the case when no_list_values == 0


mysql-test/r/partition.result:
  Added a couple of new test cases
mysql-test/t/partition.test:
  Added a couple of new test cases
sql/partition_info.cc:
  Rearranged some code to handle case where no_list_values == 0 which
  happens when one partition with only one value == NULL.
sql/sql_partition.cc:
  Rearranged code to remove compiler warning and also since we
  now have handled the case where no_list_values == 0 in a special
  case before coming here
  Added code for handling the special case where no_list_values == 0