[truetype] Some fixes for VF checks. Reported as https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=10317 * src/truetype/ttgxvar.c (ft_var_load_gvar): Properly exit memory frame if we have invalid glyph variation data offsets. (tt_face_vary_cvt): Protect against missing `tuplecoords' array. Fix typo.