Hive.getPartitionsByNames should not enforce SessionState to be available

HIVE-24743, HIVE-24392 is enforcing to check for valid write Id list for "Hive.getPartitionsByName".

This breaks basic API integration. For a user who needs to get basic partition detail, he is forced to have SessionState.

Request in this ticket is to ensure that if SessionState.get() is null, it should return empty validWriteIdList.