SDL_StretchSurface's documentation is outdated

[Slartibarty]

The comment above SDL_StretchSurface explains that srcrect and dstrect may not be NULL, but the actual implementation has code that handles this situation in a similar fashion to SDL_BlitSurfaceScaled. The comment is correct for SDL2, but the behaviour changed at some point for SDL3.

The docs:

 * \param srcrect the SDL_Rect structure representing the rectangle to be
 *                copied, may not be NULL.
 * \param dst the SDL_Surface structure that is the blit target.
 * \param dstrect the SDL_Rect structure representing the target rectangle in
 *                the destination surface, may not be NULL.

The code (same for both rects):

    if (dstrect) {
        if ((dstrect->x < 0) || (dstrect->y < 0) ||
            ((dstrect->x + dstrect->w) > dst->w) ||
            ((dstrect->y + dstrect->h) > dst->h)) {
            return SDL_SetError("Invalid destination blit rectangle");
        }
    } else {
        full_dst.x = 0;
        full_dst.y = 0;
        full_dst.w = dst->w;
        full_dst.h = dst->h;
        dstrect = &full_dst;
    }

[slouken]

Fixed, thanks!