font/sfnt: fix proprietary fonts and cmap format 12.

Two recent commits ("proprietary fonts" and "cmap format 12") each
passed all of its own tests, but the combination wasn't tested until
both were submitted.

Change-Id: Ic4c2ae8deb1e4623ca5543672dc46d55bfce91a4
Reviewed-on: https://go-review.googlesource.com/36372
Reviewed-by: David Crawshaw <crawshaw@golang.org>
2 files changed