Fix #144840: Crash unlinking object from outliner unused data mode

When unlinking object from unused data display mode, crash occurred due
to dangling pointer (`id->lib->runtime`) of parent tree element. Here
parent is "Objects" tree element which is not an actual ID. Similar to
other unlink callback, add an extra check to ensure we're unlinking from
valid ID/tree element.

Pull Request: https://projects.blender.org/blender/blender/pulls/144853

source/blender/editors/space_outliner/outliner_tools.cc

@@ -437,6 +437,10 @@ static void unlink_object_fn(bContext *C,
                              TreeStoreElem *tselem)
 {
   if (tsep && tsep->id) {
+
+    if (!TSE_IS_REAL_ID(tsep)) {
+      return;
+    }
     Main *bmain = CTX_data_main(C);
     Object *ob = (Object *)tselem->id;
     const eSpaceOutliner_Mode outliner_mode = eSpaceOutliner_Mode(