Disable wall corner rounding in legacy scenarios

[daerogami]

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This is an item logged from the To-Do and was originally reported by ADoS. If you are familiar with or can recreate this bug, please provide details here

[CelticMinstrel]

If I recall correctly, the motivation for this was that the wall corner rounding was actually broken in the original engine. Or, perhaps it was applied only if you used the built-in wall graphics, but now it's applied to even custom wall graphics.