revision: avoid leak when preparing bloom filter for "/"

If we're given an empty pathspec, we refuse to set up bloom filters, as
described in f3c2a36810 (revision: empty pathspecs should not use Bloom
filters, 2020-07-01).

But before the empty string check, we drop any trailing slash by
allocating a new string without it. So a pathspec consisting only of "/"
will allocate that string, but then still cause us to bail, leaking the
new string. Let's make sure to free it.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

revision.c

@@ -702,6 +702,7 @@ static void prepare_to_use_bloom_filter(struct rev_info *revs)
 	len = strlen(path);
 	if (!len) {
 		revs->bloom_filter_settings = NULL;
+		free(path_alloc);
 		return;
 	}