PotionSplashEvent fixes

WorldGuard cancells PotionSplashEvent if potion affect any entity. It's problem, while developing grenades etc.
EDIT:
https://github.com/Bukkit/Bukkit/blob/master/src/main/java/org/bukkit/event/entity/PotionSplashEvent.java#L71
WorldGuard sets intensity to 0 if entity is at region with potion-splash set to deny and bukkit deletes entity from affected entities list.