BPoseView::AttributeChanged(): additional check in icon case

Model::AttrChanged() requires the model to be open and so does
IconCache::IconChanged(), so add the check. Not sure if the block is
ever executed now (or ever worked before). This does at least prevent
asserts being triggered when compiled with debugging enabled.

src/kits/tracker/PoseView.cpp

@@ -5596,6 +5596,7 @@ BPoseView::AttributeChanged(const BMessage* message)
 	message->FindString("attr", &attrName);
 
 	if (TargetModel() != NULL && *TargetModel()->NodeRef() == itemNode
+		&& TargetModel()->IsNodeOpen()
 		&& TargetModel()->AttrChanged(attrName)) {
 		// the icon of our target has changed, update drag icon
 		// TODO: make this simpler (ie. store the icon with the window)