`RawImageDataU16::scaleValues_SSE2()`: avoid touching padding
`RawImageDataU16::scaleValues_SSE2()`: avoid touching padding

Now, this is indeed a breaking change, and now up to 7 last columnts
may end up being unscaled. This is not good, but we also can't really
touch that padding, asan complains. Perhaps there needs to be two types
of padding.

darktable-org/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed