const NOTDEF_GLYPH: &[u8];
Simulated .notdef glyph, same as FreeType:
0 333 hsbw endchar
See https://gitlab.freedesktop.org/freetype/freetype/-/blob/80a507a6b8e3d2906ad2c8ba69329bd2fb2a85ef/src/type1/t1load.c#L2192