According to the documentation, the functions `FT_Set_Named_Instance`,
`FT_Set_MM_Design_Coordinates`, `FT_Set_Var_Design_Coordinates`, and
`FT_Set_Var_Blend_Coordinates` can unset the `FT_FACE_FLAG_VARIATION` flag.
(The same is true for `FT_Set_MM_WeightVector` but this information was
accidentally omitted from the documentation.)
However, if a call of these functions didn't change the axis values this
could fail because internal shortcuts exited too early.
This commit reorganizes the code to handle `FT_FACE_FLAG_VARIATION` in the
top-level API functions, also taking care of the issue at hand.
* src/base/ftmm.c (FT_Set_MM_Design_Coordinates, FT_Set_MM_WeightVector,
FT_Set_Var_Design_Coordinates, FT_Set_MM_Blend_Coordinates,
FT_Set_Var_Blend_Coordinates): Handle `FT_FACE_FLAG_VARIATION`.
* src/truetype/ttgxvar.c (TT_Set_MM_Blend, TT_Set_Var_Design,
TT_Set_Named_Instance) Don't handle `FT_FACE_FLAG_VARIATION`.
* src/type1/t1load.c (T1_Set_MM_Blend, T1_Set_MM_WeightVector,
T1_Set_MM_Design): Ditto.
* src/cff/cffobjs.c (cff_face_init): Use `FT_Set_Named_Instance` instead of
low-level functions.
* src/truetype/ttobjs.c (tt_face_init): Ditto.
6713b1e41a