[OTS] Fix incorrect parsing/validation of the empty CFF index
[OTS] Fix incorrect parsing/validation of the empty CFF index

Don't add extra 2bytes when parsing an empty INDEX.

BUG=chromium:106651
TEST=ran test_{un,}malicious_fonts.sh

Review URL: http://codereview.chromium.org/8953024/



anthrotype/ots,irori/ots,irori/ots,davelab6/ots,khaledhosny/ots,anthrotype/ots,davelab6/ots