Simplify isOnline() logic.

src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java

@@ -105,13 +105,7 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
     }
 
     public boolean isOnline() {
-        for (Object obj : server.getHandle().players) {
-            EntityPlayer player = (EntityPlayer) obj;
-            if (player.getName().equalsIgnoreCase(getName())) {
-                return true;
-            }
-        }
-        return false;
+        return server.getPlayer(getUniqueId()) != null;
     }
 
     public InetSocketAddress getAddress() {