[ots] Check the presence of color bitmap tables
[ots] Check the presence of color bitmap tables

Check that the font actually contains the tables, not just that the
client requested we keep them. Sigh!

Related to #9.

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