This is better behaviour than exiting with an error.
* include/freetype/internal/tttypes.h (TT_Face): Add `use_fvar'
field.
* src/sfnt/sfobjs.c (sfnt_init_face): Compute `use_fvar', also
updating the validation code.
Use `use_fvar' to compute FT_FACE_FLAG_MULTIPLE_MASTERS.
* src/truetype/ttgxvar.c (TT_Get_MM_Var): Remove `fvar' validation
code.