In init_prepare_fake_select_lex() don't empty ftfunc_list. UNION's ORDER BY clause may 
contain MATCH(...), for which fix_index() should be called.


mysql-test/r/fulltext_order_by.result:
  BUG#11869 part2 : added another test case
mysql-test/t/fulltext_order_by.test:
  BUG#11869 part2 : added another test case