resolves #2460

1. Hit entity when entity is invisble in 3 cases
   a. when using projectiles spells
   b. when using aoe spells
   c. when using single target spell on a visible player, but there is player in stealth inside hit radius
2. Dont keep looking at the entity if the entity is invisible
3. If there is another valid target on range when the current target becomes invisible, change target.