Fix NPE when custom code changes a player's HP (#458)

src/client/MapleCharacter.java

@@ -8605,9 +8605,10 @@ public class MapleCharacter extends AbstractMapleCharacterObject {
                 }
             }
         };
-        
+        if (map != null) {
             map.registerCharacterStatUpdate(r);
 	}
+    }
     
     private Pair<MapleStat, Integer> calcHpRatioUpdate(int newHp, int oldHp) {
         int delta = newHp - oldHp;