Merge branch 'jk/commit-graph-slab-clear-fix'

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

Author: gitster

commit-graph.c

@@ -806,6 +806,9 @@ 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;

t/t5510-fetch.sh

@@ -803,7 +803,8 @@ test_expect_success 'fetch.writeCommitGraph with submodules' '
 		cd super-clone &&
 		rm -rf .git/objects/info &&
 		git -c fetch.writeCommitGraph=true fetch origin &&
-		test_path_is_file .git/objects/info/commit-graphs/commit-graph-chain
+		test_path_is_file .git/objects/info/commit-graphs/commit-graph-chain &&
+		git -c fetch.writeCommitGraph=true fetch --recurse-submodules origin
 	)
 '