This is aimed at providing a little quality of life in the form of not
having to divest yourself of your sources of magic resistance before
using a level teleporter. The player is already able to use regular
teleport traps while Antimagic; there's no reason why it should be
different for level teleporters.
This ultimately comes from "Stevie-O's level teleporter jump patch", by
way of SliceHack. I simplified it a bit: deliberately jumping onto the
trap always takes time even if it fails to levelport you (which would
only happen with level teleporters in the End Game, which don't exist).
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