[libgdx] Improved AnimationState behavior when paused.

Ie, when time scale is 0 or `update(0)` is used.

* Better check for whether the from entry has been applied at least once.
* Discard the from entry if both the from and to entries haven't advanced. Ie, the mix hasn't started for the from entry.

spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/AnimationState.java

@@ -180,16 +180,18 @@ public class AnimationState {
 		from.animationLast = from.nextAnimationLast;
 		from.trackLast = from.nextTrackLast;
 
-		// Require mixTime > 0 to ensure the mixing from entry was applied at least once.
-		if (to.mixTime > 0 && to.mixTime >= to.mixDuration) {
-			// Require totalAlpha == 0 to ensure mixing is complete, unless mixDuration == 0 (the transition is a single frame).
-			if (from.totalAlpha == 0 || to.mixDuration == 0) {
-				to.mixingFrom = from.mixingFrom;
-				if (from.mixingFrom != null) from.mixingFrom.mixingTo = to;
-				to.interruptAlpha = from.interruptAlpha;
-				queue.end(from);
+		if (to.nextTrackLast != -1) { // The from entry was applied at least once.
+			boolean discard = to.mixTime == 0 && from.mixTime == 0; // Discard the from entry when neither have advanced yet.
+			if (to.mixTime >= to.mixDuration || discard) {
+				// Require totalAlpha == 0 to ensure mixing is complete or the transition is a single frame or discarded.
+				if (from.totalAlpha == 0 || to.mixDuration == 0 || discard) {
+					to.mixingFrom = from.mixingFrom;
+					if (from.mixingFrom != null) from.mixingFrom.mixingTo = to;
+					to.interruptAlpha = from.interruptAlpha;
+					queue.end(from);
+				}
+				return finished;
 			}
-			return finished;
 		}
 
 		from.trackTime += delta * from.timeScale;