Fix incorrect type cast of Outliner view layer element data

The view layer "base" element (the parent that the individual layers are
nested in) does not point to any data in its `directdata`, definitely
not to a view layer. Don't cast it to one, this can cause undefined
behavior when the pointer is not null.

source/blender/editors/space_outliner/outliner_select.cc

@@ -1345,7 +1345,6 @@ static void outliner_set_properties_tab(bContext *C, TreeElement *te, TreeStoreE
         context = BCONTEXT_DATA;
         break;
       }
-      case TSE_R_LAYER_BASE:
       case TSE_R_LAYER: {
         ViewLayer *view_layer = static_cast<ViewLayer *>(te->directdata);