When iterating over the cvt tuples and reading in the points it is necessary
to set all of `localpoints`, `points`, and `point_count` in all cases. The
existing code did not reset `localpoints` to `NULL` when there were no
private point numbers. If the previous tuple did have private point numbers
and set `localpoints` to `ALL_POINTS` this would not be cleared and the
wrong branch would be taken later, leading to possible heap buffer overflow.
* src/truetype/ttgxvar.c (tt_face_vary_cvt): Reset `localpoints` to `NULL`
when it isn't valid.
Fixes: https://crbug.com/1284742
afb4ca0151