Allow "no glyphs" check in TTF save to see glyph 0
Corrects issue in which a font with exactly one glyph, no ".notdef", generates
a spurious "no glyphs" warning on Generate of TTF or OTF.
Merge pull request #204 from mskala/check_zero_glyph

Allow "no glyphs" check in TTF save to see glyph 0