This prevents SDL from making an OpenGL context and maybe throwing it away
immediately by default. It will now only do it when trying to request a
window framebuffer directly, or creating an SDL_Renderer with the "software"
backend, which makes that request itself.
The way SDL decides if it should use a "texture framebuffer" needs dramatic
updating, but this solves the immediate problem.
Reference Issue #4624.
f37e4a94d3