Fix some bugs relating to the use of buffers
in the overlay frames.

Fix bug where a mid sequence overlay was
propagating large partition and transform sizes into
the subsequent frame because of :-
  sf->last_partitioning_redo_frequency  > 1 and
  sf->tx_size_search_method == USE_LARGESTALL

Change-Id: Ibf9ef39a5a5150f8cbdd2c9275abb0316c67873a