Determine the possibility of context loss in SDL2

[nukep]

As I understand it, OpenGL context losses aren't a real issue on the vast majority of platforms that SDL2 supports. However, the issue reportedly arises on Android and EGL if the device wakes up after going to sleep. I don't know for certain if this can happen in the Android port of SDL2, but it probably can. The issue might also show up on SDL2 with Emscripten + WebGL, but I'm unsure.

If context losses are indeed possible in SDL2, detect it and acknowledge it with an error in swap_buffers().

From #3