philips: Clip extra padding in downsampled levels
philips: Clip extra padding in downsampled levels

We can't remove the padding in level 0 because we don't know how much
there is, but we can prevent the padding from becoming more pronounced
in downsampled levels.  Subtract the excess from the level dimensions
and clip it out when drawing.

openslide/openslide,openslide/openslide,openslide/openslide,openslide/openslide