Engine: fix regressions with clipupdatesector() from df868267

This resolves a bug in Duke3D where the player couldn't move while shrunk if a TROR sector was present on the map.

Map that demonstrates the issue: tror_shrunk_stuck.map

It still preserves the fix to allow actors to properly cross TROR layers:tror-lizman.map

It also ensures that the original clipping is used if no TROR bunch is present inside the sector in question. This should reduce the amount of backwards-compatibility problems.

For instance, in AMC, a ship sprite would collide with a ceiling where it did not before, breaking a scripted sequence. (I'm actually not 100% sure if that was an accidental bugfix, it seems related to how the drones in Duke3D can just ascend above the ceiling and become unhittable. In any case, this change preserves the original behavior.)