rasterizer: fix assembly for WIN64
rasterizer: fix assembly for WIN64

Second argument of cglobal macro for fill_halfplane in 64-bit mode
should always be 6 to preload all function arguments into registers.
It doesn't matter under *nix as the first 6 arguments are already
in registers according to calling conventions, but under WIN64
it's only the first 4.

libass/libass,ShiftMediaProject/libass,libass/libass,MrSmile/libass,ShiftMediaProject/libass,astiob/libass,xbmc/libass,astiob/libass,MrSmile/libass,xbmc/libass