tiff/lzw: sync (yet again) to the upstream lzw in the stdlib.

This picks up a recent change:
https://go-review.googlesource.com/#/c/11661/

Change-Id: I0309f7b804e0d88ea623c8ae97b65cd0c2bad101
Reviewed-on: https://go-review.googlesource.com/11850
Reviewed-by: David Symonds <dsymonds@golang.org>
1 file changed