Outliner: Fix crash on duplicating scene

The function to determine if a collection was hidden was missing
a check to see if the layer collection was not null.

source/blender/blenkernel/intern/layer.c

@@ -515,7 +515,7 @@ static bool layer_collection_hidden(ViewLayer *view_layer, LayerCollection *lc)
     if (parent) {
       lc = BKE_layer_collection_first_from_scene_collection(view_layer, parent->collection);
 
-      return layer_collection_hidden(view_layer, lc);
+      return lc && layer_collection_hidden(view_layer, lc);
     }
     else {
       return false;