Bug fixes for the lava puzzle

### Boats don't collide
* since the boats are not moved via WalkActorTo but via SetActorAt, handleCollisionWith() was never called and so the LUA callback to handle the collision was not called as well
* simple bug fix: call handleCollisionWith() in Actor::setPos(), too - this  fixes #877 

### Boats are invisible
* running residualvm via apitrace revealed, that the boat's vertices consisted of just NaNs and so they were ignored by the OpenGL implementation
* they were computed using quats which contained just NaNs which were computed by normalizing a (0, 0, 0, 0) quat (which is basically a division by zero)
* commit b1af372 fixes this issue (#1107)