[sfnt] Avoid undefined shifts in `COLR` v1 paint parsing

* src/sfnt/ttcolr.c (read_paint, tt_face_get_paint): Tighten shift
behavior by using multiplication, mostly using macros from ftcalc.h.

Fixes: https://bugs.chromium.org/p/chromium/issues/detail?id=1269168
1 file changed