statement from a UNION query with ORDER BY an expression containing
RAND().
The crash happened because the global order by list in the union query
was not re-initialized for execution.
(Local order by lists were re-initialized though).



mysql-test/r/ps.result:
  Added a test case for bug #27937.
mysql-test/t/ps.test:
  Added a test case for bug #27937.
sql/sql_union.cc:
  Fixed bug #27937: crash for the the second execution of a prepared
  statement from a UNION query with ORDER BY an expression containing
  RAND().
  The crash happened because the global order by list in the union query
  was not re-initialized for execution.
  (Local order by lists were re-initialized though).
  Added re-initialization of the global order by list in the function
  st_select_lex_unit::init_prepare_fake_select_lex.