Add missing UserManager check

Caused an java.lang.IndexOutOfBoundsException: Index: 0

Fixes #2335

src/main/java/com/gmail/nossr50/skills/taming/TrackedTamingEntity.java

@@ -52,6 +52,10 @@ public class TrackedTamingEntity extends BukkitRunnable {
             CombatUtils.dealDamage(livingEntity, livingEntity.getMaxHealth(), DamageCause.SUICIDE, livingEntity);
         }
 
+        if (!UserManager.hasPlayerDataKey(owner)) {
+            return;
+        }
+
         McMMOPlayer mcMMOPlayer = UserManager.getPlayer(owner);
         TamingManager tamingManager = mcMMOPlayer.getTamingManager();