sw_engine: fix the inproper stroke raster.

sw_engine: fix the inproper stroke raster.

We have an incorrect value comparison when the stroke corner center
is adjusted. All coordinates in the stroke raster have been scaled by
the given values (sx, sy), while the stroke width remains at its
original size due to it not being clear how it should be scaled.

This brings wierd rendering results at times. Now fix it.

@Issue: https://github.com/thorvg/thorvg/issues/1336

Change-Id: If7a76a5fe5ddb52292903b68cfde951f95e3e5f2
Signed-off-by: jykeon <jykeon@samsung.com>