Fixes intermittent teleport-to-(0,0) bullet issue. Dead shields were still being...

Fixes intermittent teleport-to-(0,0) bullet issue. Dead shields were still being notified to act(), despite being correctly removed from all the bookkeeping locations (pathmap, game, etc) ... except owner.components. This itself would have just been a memory leak except that act() did not test whether the shield was alive. So when a dead shield would move, it could still hit things--it was only looking for things to hit and not testing if it was itself dead. These phantom collisions would result in NaN coords, which becomes 0 when coerced to int by DOMElement. Bam.