Improve error description for missing effect.

Assets/Cryville/Crtr/EffectManager.cs

@@ -1,4 +1,6 @@
+using Cryville.Common;
 using Cryville.Common.Collections.Specialized;
+using System;
 using UnityEngine;
 
 namespace Cryville.Crtr {
@@ -14,10 +16,15 @@ namespace Cryville.Crtr {
 			foreach (var g in _groups) g.Value.Tick(time);
 		}
 		public void Emit(int id, float index) {
-			_groups[id].Emit(index);
+			GetGroup(id).Emit(index);
 		}
 		public void EmitSelf(int id, float index, Transform target) {
-			_groups[id].Emit(index, target);
+			GetGroup(id).Emit(index, target);
+		}
+		EffectGroup GetGroup(int id) {
+			EffectGroup result;
+			if (_groups.TryGetValue(id, out result)) return result;
+			throw new ArgumentException(string.Format("The effect \"{0}\" is not found", IdentifierManager.Shared.Retrieve(id)));
 		}
 		public void Dispose() {
 			foreach (var g in _groups) g.Value.Dispose();