Fix player null check in location runnable

src/main/java/wtf/beatrice/limbomanager/objects/LocationCheckRunnable.java

@@ -32,9 +32,15 @@ public class LocationCheckRunnable implements Runnable
             return;
         }
 
-        Player player = playersToCheck.get(0);
+        // load the player
+        Player player = null;
+        while(player == null || !player.isOnline()) // check if player left and in case, move to next one
+        {
+            player = playersToCheck.get(0);
+            playersToCheck.remove(player);
+        }
+
         Location playerLocation = player.getLocation();
-        playersToCheck.remove(player);
 
         Coordinates playerIslandCoordinates = Cache.playerIslands.get(player.getName());