WORLDGUARD-3978 - Reported by Princeps

Calling WorldGuardPlugin#wrapOfflinePlayer(org.bukkit.OfflinePlayer) throws an Nullpointer, because BukkitOfflinePlayer invokes the constructor of BukkitPlayer with super(null, null).
In the constructor is not checked, if the passed parameter is null - its simply called null.getName() (expected an player, not null).

Quick Fix: Add a check around the Player.getName() call.
However, I dont know if this breaks anything else.