[sfnt] Avoid undefined shifts in `COLR` v1 color line retrieval

* src/sfnt/ttcolr.c (tt_face_get_colorline_stops): Disambiguate shift
behavior by using multiplication using macros from ftcalc.h.

Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=50573
1 file changed