Martin Storsjö authored Nov 20, 2018 and Jean-Baptiste Kempf committed Nov 20, 2018

This fixes compiler errors like these:
src/film_grain_tmpl.c(238): error C2036: 'void *': unknown size

Don't rely on sizeof(void) == 1 in pointer arithmetic, but instead
cast the row pointers to the pixel datatype immediately, use PXSTRIDE()
for converting a stride in byte units to pixel units, and skip
sizeof(pixel) for horizontal offsets that previously were applied on
a void pointer.