Don't perform glCopyTextImage with coordinates outside the buffer.

    Rect bounds(left, top, right, bottom);

    if (!fboLayer) {

        mSnapshot->transform->mapRect(bounds);

        // Layers only make sense if they are in the framebuffer's bounds

        bounds.intersect(*mSnapshot->clipRect);

        // When the layer is not an FBO, we may use glCopyTexImage so we

        // need to make sure the layer does not extend outside the bounds

        // of the framebuffer

        bounds.intersect(snapshot->previous->viewport);

        // We cannot work with sub-pixels in this case

        bounds.snapToPixelBoundaries();

    }