vp8l: don't ignore I/O errors when reading LZ77 parameters.

Fixes golang/go#10383

Change-Id: I3e5e357a40a45189c31f0b4db9422dedc351c910
Reviewed-on: https://go-review.googlesource.com/9912
Reviewed-by: Nigel Tao <nigeltao@golang.org>
1 file changed