Changed the way zombie speed is calculated. This should stop zombies from being faster than intended

IndieStone has changed the functionality of getZombieLungeSpeed. Mod now uses getSpeedMod to determine speed.

Added zombie:getTarget() to fix nil pointer.

Added a small check to prevent having zombies having no target.

update 1:
* Fixed TargetVelocity.
* Lunging zombies only anticipate when then are near you, should prevent slow shamblers from attempting to out manouver you while being 10 meters away...
* While trying to run past zombies, the zombies should move more towards you instead of only cutt ing off your route