[OTS] sanitizer incorrectly rejects fonts with optical size feature ('size')
[OTS] sanitizer incorrectly rejects fonts with optical size feature ('size')

Fix a wrong calculation of FeatureTable length.
The patch is provided by jfkthame.

TEST=ran test_{un,}malicious_fonts.sh
BUG=104389


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