Add animation stub and effect stub for skin.

Assets/Cryville/Crtr/PropSrc.cs

@@ -43,6 +43,7 @@ namespace Cryville.Crtr {
 				buf[0] = _cb() ? (byte)1 : (byte)0;
 			}
 		}
+		public static readonly PropSrc Error = new Arbitrary(PdtInternalType.Error, new byte[0]);
 		public class Float : FixedBuffer {
 			readonly Func<float> _cb;
 			public Float(Func<float> cb) : base(PdtInternalType.Number, 4) { _cb = cb; }