Image upscale crash (bounds unchecked).

Specific commit:

https://github.com/qtproject/qtbase/commit/7432c7c08a6709a12a143d48fbaa9927962edae8#diff-85cfebdfa5006b891e2ea682ae923325L375

introduces undefined behaviour because of getting out of bounds.

Previously there was "if(XAP > 0){" condition and only in that case we dereferenced both "pix" and "pix+1", which was not evaluated when "y == dh - 1 && x == end - 1", and if "XAP == 0" just value of "pix" (equal to "&sptr[xpoints[x] ]" equal to "ypoints[dyy + y] + xpoints[x]") was used.

But after that commit it was replaced by a short:

for (int x = dxx; x < end; x++) {
    const unsigned int *pix = sptr + xpoints[x];
    const int xap = xapoints[x];
    *dptr = INTERPOLATE_PIXEL_256(pix[0], 256 - xap, pix[1], xap);
    dptr++;
}

in which we always look at pix[1] even if pix is already pointing to the last allocated int (and is not used, because xap is zero and pix[1] is multiplied by zero), which causes undefined behaviour and crashes in OS X (at least).