SUBSELECT_HASH_SJ_ENGINE::CLEANUP

ISSUE: For processing the query, creation of myisam
       temporary table fails since the key length in the
       query is larger than the supported length.
       Further in cleanup, variables which are not allocated
       due to the above reason are attempted to free up
       resulting in server to exit abnormally.

FIX: Server will return error if unable to create
     temporary table for query processing.
     Added checks in cleanup to check if variables
     are actually allocated before freeing up.