Outliner: Fix useless assert in new liboverride showing code.

It is perfectly 'valid' to find invalid RNA properties references in
override properties list. Data change, RNA changes, IDProperties change,
some linked ID may become unavailable, etc.

Note that those invaldi override properties are cleaned up when updating
the override info (so typically on undo step storage, and .blend file save).

source/blender/editors/space_outliner/outliner_tree.c

@@ -655,7 +655,9 @@ static void outliner_add_library_override_contents(SpaceOutliner *soops, TreeEle
   int index = 0;
   LISTBASE_FOREACH (IDOverrideLibraryProperty *, op, &id->override_library->properties) {
     if (!BKE_lib_override_rna_property_find(&idpoin, op, &override_ptr, &override_prop)) {
-      BLI_assert(false);
+      /* This is fine, override properties list is not alwasy fully up-to-date with current
+       * RNA/IDProps etc., this gets cleaned up when re-generating the overrides rules, no error
+       * here. */
       continue;
     }