repository: fix repo_init() memleak due to missing _clear()

There is an old pre-existing memory leak in repo_init() due to failing
to call clear_repository_format() in the error case.

It went undetected because a specific bug is required to trigger it:
enable a v1 extension in a repository with format v0. Obviously this
can only happen in a development environment, so it does not trigger
in normal usage, however the memleak is real and needs fixing.

Fix it by also calling clear_repository_format() in the error case.

Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

repository.c

@@ -298,6 +298,7 @@ int repo_init(struct repository *repo,
 	return 0;
 
 error:
+	clear_repository_format(&format);
 	repo_clear(repo);
 	return -1;
 }