In function:
int
SDL_UpperBlitScaled(SDL_Surface * src, const SDL_Rect * srcrect,
              SDL_Surface * dst, SDL_Rect * dstrect)
{
   //Some Code
   /* If the destination rectangle is NULL, use the entire dest surface */
    if (dstrect == NULL) {
        fulldst.x = fulldst.y = 0;
        dstrect = &fulldst;
    }
   //Some Code
   /* clip the destination rectangle against the clip rectangle */
    if (dstrect) {
        int maxw, maxh;

        final_dst.x = dstrect->x;
        final_dst.w = dstrect->w;
        if (final_dst.x < 0) {
            final_dst.w += final_dst.x;
            final_dst.x = 0;
        }
        maxw = dst->w - final_dst.x;
        if (maxw < final_dst.w)
            final_dst.w = maxw;

        final_dst.y = dstrect->y;
        final_dst.h = dstrect->h;
        if (final_dst.y < 0) {
            final_dst.h += final_dst.y;
            final_dst.y = 0;
        }
        maxh = dst->h - final_dst.y;
        if (maxh < final_dst.h)
            final_dst.h = maxh;
    } else {
        final_dst.x = final_dst.y = 0;
        final_dst.w = dst->w;
        final_dst.h = dst->h;
    }
   //Some Code
}

In This code there is no need of if-else statement for dstrect, because it's handling has already been done. 
So remove this if-else statement and remove the else part from the code.