Method check

src/main/java/trace/graphics/GL.java:23–26

(Runnable o)

	}

	private static void check(Runnable o) {
		check(GraphicsContext.getContext() != null);
		o.run();
	}

	private static <T> T check2(Callable<T> o) {
		check(GraphicsContext.getContext() != null);