This bug was intruduced by the fix for bug#17212 (in 4.1). It is not 
ok to call test_if_skip_sort_order since this function will 
alter the execution plan. By contract it is not ok to call 
test_if_skip_sort_order in this context.

This bug appears only in the case when the optimizer has chosen 
an index for accessing a particular table but finds a covering 
index that enables it to skip ORDER BY. This happens in 
test_if_skip_sort_order.


mysql-test/r/key.result:
  Bug#24778
  
  test case.
  
  The bug causes the result to be the empty set.
mysql-test/t/key.test:
  Bug#24778
  
  The minimal test case that reveals the bug. The reason for such a 
  complicated schema is that we have to convince the optimizer to 
  pick one index, then discard it in order to be able to skip 
  ORDER BY.
sql/sql_select.cc:
  bug#24778
  
  Removed the call to test_if_skip_sort_order that constituted the
  bug.