We exit early if the current design or blend coordinates are
identical to the new ones.
* src/truetype/ttgxvar.c (tt_set_mm_blend, TT_Set_Var_Design):
Implement it, returning internal error code -1 if there will be no
variation change.
* src/type1/t1load.c (t1_set_mm_blend): Ditto.
* src/base/ftmm.c (FT_Set_Var_Design_Coordinates,
FT_Set_MM_Blend_Coordinates, FT_Set_Var_Blend_Coordinates): Updated.
08cd62deed