When travel is high enough, keep the global position resulting from the
move_and_collide call, and set the motion to the remainder from the
move_and_collide call. This ensures travel is taken into account once,
rather than twice.
Physics body previously stored the RID of a collision object and accessed it on the next frame, leading to a crash if the object had been deleted.
This PR checks the object still exists via the ObjectID prior to access.