Valgrind warning happens due to uninitialized cached_format_type field
which is used later in Item_func_str_to_date::val_str method.
The fix is to init cached_format_type field.


mysql-test/r/func_time.result:
  test case
mysql-test/t/func_time.test:
  test case
sql/item_timefunc.cc:
  init cached_format_type field