boyuanxiao-argondesign authored Oct 15, 2018 and Ronald S. Bultje committed Nov 14, 2018

The previous code raised an error if !segmentation.update_map but the
reference frame didn't yield any segmentation data. (The first "goto
error" that the patch removes happens if the reference frame was the
right size but had no segmentation data; the second happens if the
reference frame was the wrong size).

This doesn't match the logic in the description of
load_previous_segment_ids in section 6.8.2 of the spec.

This patch allows such streams, allocating and zeroing cur_segmap in
this case. It is still an error for a stream to signal a temporal
update but not to have valid segmentation data from the ref frame -
that's the error case that the patch puts back in.