crash

resolve_const_item() substitutes item which will evaluate to constant with
equvalent constant item, basing on the item's result type. In this case
subselect was resolved as constant, and resolve_const_item() was substituting
it's result's Item_caches to Item_null. Later Item_cache's function was called
for Item_null object, which caused server crash.

resolve_const_item() now substitutes constants for items with 
result_type == ROW_RESULT only for Item_rows.


sql/item.cc:
  Fix bug #14482 Wrongly applied optimization in resolve_const_item() caused
  crash
  
  resolve_const_item() now applies optimization for items with
  result_type == ROW_RESULT only to Item_rows.
mysql-test/t/select.test:
  Test case for bug #14482 Wrongly applied optimization in resolve_const_item() caused crash
mysql-test/r/select.result:
  Test case for bug #14482 Wrongly applied optimization in resolve_const_item() caused crash