Merge pull request #759 from inguin/emi-fixes

EMI: Various small bugfixes
EMI: Keep actor position after detaching
EMI: Use WorldPos in Lua_V1::GetActorSector

In mot.set, Guybrush is attached to a raft at position (0,0,0).
This commit solves one instance of the camera going back to the first
screen.
EMI: Return to original sort order when no sort plane is available

The floor in the Hall of Justice is hidden by a solid gray actor named
"trap plane". This actor is originally positioned far in the background
but moved to the foreground because we can't find a sort plane in the
sector.

This patch stores returns an actor to the original sort order set by
the game script when entering a sector that has no sort information.