partition if muliple columns used

Problem was that range scanning through the sorted array of
the column list values did not use a correct index calculation.

Fixed by also taking the number of columns in the calculation.

mysql-test/r/partition_column.result:
  Bug#52815: LIST COLUMNS doesn't insert rows in correct
             partition if muliple columns used
  
  Added test result for bug.
mysql-test/t/partition_column.test:
  Bug#52815: LIST COLUMNS doesn't insert rows in correct
             partition if muliple columns used
  
  Added test for bug.
sql/sql_partition.cc:
  Bug#52815: LIST COLUMNS doesn't insert rows in correct
             partition if muliple columns used
  
  list_col_array is a matrix of field values, so one must also
  use the number of columns to calculate the correct partition
  id.