Fix CFF parsing with charset format 0 and FDArray format 0

The code for those two was using the variable glyphs, but glyphs
was only initialized when CharStrings was read, which is typically
after the other ones.  Use num_glyphs from maxp instead, and add
checks to make sure it matches the one from CharStrings.
Drop -Werror

Whoever wants it should set it locally.