[c] Fixes #1282, animation state was missing a null check when iterating mixed out track entries.

spine-c/spine-c/src/spine/AnimationState.c

@@ -862,6 +862,7 @@ void _spAnimationState_animationsChanged (spAnimationState* self) {
 
 	for (;i < n; i++) {
 		entry = self->tracks[i];
+		if (!entry) continue;
 		while (entry->mixingFrom != 0)
 			entry = entry->mixingFrom;
 		do {