Fix for Floating Actors (0.23.2 Alpha)

I discovered some odd circumstances where Actors would simply float in the air, unaffected by physics.  As it turns out, I left out a check for a flag I was setting to stop the code from continuing to branch out, so the terrain was getting updated more than required, producing strange results.

This resulted in Actors sometimes being treated as though they were buried under blocks when they weren't.

This is now fixed.

I really, really hope this is the last time I have to touch Actor physics code for quite a while, because I'm sick of it.