[csharp] Port of commit d9b882e. Added TrackEntry.IsEmptyAnimation.

spine-csharp/src/AnimationState.cs

@@ -40,7 +40,7 @@ namespace Spine {
 	/// See <a href='http://esotericsoftware.com/spine-applying-animations/'>Applying Animations</a> in the Spine Runtimes Guide.</para>
 	/// </summary>
 	public class AnimationState {
-		static readonly Animation EmptyAnimation = new Animation("<empty>", new ExposedList<Timeline>(), 0);
+		internal static readonly Animation EmptyAnimation = new Animation("<empty>", new ExposedList<Timeline>(), 0);
 
 		/// 1) A previously applied timeline has set this property.<para />
 		/// Result: Mix from the current pose to the timeline pose.
@@ -1253,6 +1253,10 @@ namespace Spine {
 		/// If true, the animation will be applied in reverse. Events are not fired when an animation is applied in reverse.</summary>
 		public bool Reverse { get { return reverse; } set { reverse = value; } }
 
+		/// <summary>Returns true if this entry is for the empty animation. See <see cref="AnimationState.SetEmptyAnimation(int, float)"/>,
+		/// <see cref="AnimationState.AddEmptyAnimation(int, float, float)"/>, and <see cref="AnimationState.SetEmptyAnimations(float)"/>.
+		public bool IsEmptyAnimation { get { return animation == AnimationState.EmptyAnimation; }}
+
 		/// <summary>
 		/// <para>
 		/// Resets the rotation directions for mixing this entry's rotate timelines. This can be useful to avoid bones rotating the