[csharp] Ported active bone check in SkeletonBounds. See #1378.

spine-csharp/src/SkeletonBounds.cs

@@ -74,6 +74,7 @@ namespace Spine {
 
 			for (int i = 0; i < slotCount; i++) {
 				Slot slot = slots.Items[i];
+				if (!slot.bone.active) continue;
 				BoundingBoxAttachment boundingBox = slot.attachment as BoundingBoxAttachment;
 				if (boundingBox == null) continue;
 				boundingBoxes.Add(boundingBox);