possible null pointer dereference in sfRenderTexture_destroy

[ZXShady]

void sfRenderTexture_destroy(const sfRenderTexture* renderTexture)
{
    delete renderTexture->Target;
    delete renderTexture;
}

if renderTexture is null then we are dereferencing a null pointer, so I fixed it by making Target a std::unique_ptr instead of if(renderTexture) delete renderTexture->Target check and it better resembles the ownership model.