Fix #105216: Clear Asset does not immediately redraw the outliner

While **marking** an asset would update the Outliner immediately (this
due to the fact that `ED_asset_generate_preview` indirectly took care of
a refresh), **clearing** an asset would not do this.

Now be explicit about this in the Outliner listener and consider asset
notifiers there.

Pull Request: blender/blender#105287

source/blender/editors/space_outliner/space_outliner.cc

@@ -195,6 +195,11 @@ static void outliner_main_region_listener(const wmRegionListenerParams *params)
         ED_region_tag_redraw(region);
       }
       break;
+    case NC_ASSET:
+      if (ELEM(wmn->action, NA_ADDED, NA_REMOVED)) {
+        ED_region_tag_redraw_no_rebuild(region);
+      }
+      break;
     case NC_MATERIAL:
       switch (wmn->data) {
         case ND_SHADING_LINKS: