repository: free main reference database

While we release worktree and submodule reference databases when
clearing a repository, we don't ever release the main reference
database. This memory leak went unnoticed because its pointer is
kept alive by the "chdir_notify" subsystem.

Fix the memory leak.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

repository.c

diff --git a/repository.c b/repository.c
index 187dd47..e2b5c67 100644
--- a/repository.c
+++ b/repository.c
@@ -421,6 +421,11 @@ void repo_clear(struct repository *repo)
 		FREE_AND_NULL(repo->remote_state);
 	}
 
+	if (repo->refs_private) {
+		ref_store_release(repo->refs_private);
+		FREE_AND_NULL(repo->refs_private);
+	}
+
 	strmap_for_each_entry(&repo->submodule_ref_stores, &iter, e)
 		ref_store_release(e->value);
 	strmap_clear(&repo->submodule_ref_stores, 1);