It is a perfectly round Room. Nothing can make a Corner to stand in it, unless you break the exterior wall enough to force one. But by making a Corner it stops being a Round Room defeating the purpose of finding it out. It is doing nothing to whoever tries to find it. That is merely Peoples Brains overthinking it, and making a fool of themselves to try something that makes no sense. But let them try, and fail, and fail again. There is no corner, for if it had any it is not a Round Room anymore.