EMI: Fix Deadeye Dave's head

On current master, the head tracking doesn't work correctly for Deadeye Dave in the set pop. This is because SetActorHead is called with a nil value for the head offset Z coordinate, and the current implementation of SetActorHead expects all of the coordinate parameters to be proper numeric values. I changed this in 8316549 so the coordinates will default to 0 if no numeric value is given.

This also uncovered another issue. Because the head tracking was not properly initialized for Deadeye Dave, the head tracking attempted to animate a joint with an empty name. It turns out the root joint of the skeleton has an empty string for a name, so the root joint was animated, causing the whole model to rotate. This is fixed by b705450.