Merge branch 'jk/commit-graph-slab-clear-fix' into maint-2.43

Clearing in-core repository (happens during e.g., "git fetch
--recurse-submodules" with commit graph enabled) made in-core
commit object in an inconsistent state by discarding the necessary
data from commit-graph too early, which has been corrected.

* jk/commit-graph-slab-clear-fix:
  commit-graph: retain commit slab when closing NULL commit_graph

commit-graph.c

@@ -831,6 +831,9 @@ struct bloom_filter_settings *get_bloom_filter_settings(struct repository *r)
 
 void close_commit_graph(struct raw_object_store *o)
 {
+	if (!o->commit_graph)
+		return;
+
 	clear_commit_graph_data_slab(&commit_graph_data_slab);
 	free_commit_graph(o->commit_graph);
 	o->commit_graph = NULL;