Queries like:

  SELECT ROW(1, 2) IN (SELECT t1.a, 2)
    FROM t1 GROUP BY t1.a

or 

  SELECT ROW(1, 2) IN (SELECT t1.a, 2 FROM t2)
    FROM t1 GROUP BY t1.a

lead to assertion failure in the
Item_in_subselect::row_value_transformer method in debugging
build, or to unexpected error message in release build:

  ERROR 1247 (42S22): Reference '<list ref>' not supported (forward
                      reference in item list)

Unexpected error message and assertion failure have been
eliminated.


mysql-test/r/subselect3.result:
  Added test case for bug #34763.
mysql-test/t/subselect3.test:
  Added test case for bug #34763.
sql/item.cc:
  Fixed bug #34763.
  The Item_ref::fix_fields method has been modified to silently
  ignore not fixed outer references: by the definition, those
  references should be fixed later by the call to the
  fix_inner_refs function.
sql/item_subselect.cc:
  Fixed bug #34763.
  The Item_in_subselect::row_value_transformer method has been
  modified to eliminate assertion failure on not fixed outer
  references: by the definition those references are allowed in
  this context and should be fixed later by the call to the
  fix_inner_refs function.