Fixed memory overrun bug in gdImageScaleTwoPass

_gdContributionsCalc would compute a window size and then adjust
the left and right positions of the window to make a window within
that size.  However, it was storing the values in the struct *before*
it made the adjustment.  This change fixes that.
gdImagePtr gdImageScaleBilinear(gdImagePtr im, const unsigned int new_width, const unsigned int new_height)
{
	if (im->trueColor) {
		return gdImageScaleBilinearTC(im, new_width, new_height);
	} else {
		return gdImageScaleBilinearPalette(im, new_width, new_height);
	}
}

gdImagePtr gdImageScaleBilinear(gdImagePtr im, const unsigned int new_width, const unsigned int new_height)
{
	if (im->trueColor) {
		return gdImageScaleBilinearTC(im, new_width, new_height);
	} else {
		return gdImageScaleBilinearPalette(im, new_width, new_height);
	}
}
