Add missing return for known potion effects

EndlessClient/Rendering/Effects/EffectSpriteManager.cs

@@ -69,6 +69,7 @@ private IList<IEffectSpriteInfo> ResolvePotionEffect(HardCodedPotionEffect effec
                 var retList = _potionEffects[effect];
                 foreach (var item in retList)
                     item.Restart();
+                return new List<IEffectSpriteInfo>(retList);
             }
 
             // potion graphics that aren't in the hard-coded list here use the same formula as spell graphics