Duke3D: Automap overhead sprite grows when shrunk

Original Thread: https://forums.duke4.net/topic/11484-automap-glitch-with-shrunken-duke/page__gopid__354962#entry354962

Regression introduced by 86b57410.

The overhead sprite used to shrink properly along with the player, but now it grows instead, as if the player actor were close to the sector ceiling.