Patch to fix valgrind warning that uninitialized bytes were written. 
The warning was caused by set_default(), which assumes that the field pointer is pointing
into record[0], while all other functions honors the move_field_offset().


sql/log_event.cc:
  Changing unpack_row() to always unpack into table->record[0] since the Field class hierarchy
  contain too many dependencies on the record to operate on being in table->record[0].
  Changing code to use the new unpack_row(), which requires some juggling of records in
  one case.