The bug was that for ordered index scans, ha_partition::index_init() did
not put index columns into table->read_set if the underlying storage 
engine did not have HA_PARTIAL_COLUMN_READ flag. 
This was causing assertion failure when handle_ordered_index_scan() tried
to sort the records according to index order.

Fixed by making ha_partition::index_init() put index columns into table->read_set
for all ordered scans. 


mysql-test/r/partition.result:
  BUG#32772: partition crash 1: enum column
  - Testcase
mysql-test/t/partition.test:
  BUG#32772: partition crash 1: enum column
  - Testcase
sql/ha_partition.cc:
  BUG#32772: partition crash 1: enum column
  - Make ha_partition::index_init() include index columns in the read_set
    whenever an ordered scan is initialized, no matter if
    HA_PARTIAL_COLUMN_READ is set or not.