name-rev: avoid leaking memory in the `deref` case

When the `name_rev()` function is asked to dereference the tip name, it
allocates memory. But when it turns out that another tip already
described the commit better than the current one, we forgot to release
the memory.

Pointed out by Coverity.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/name-rev.c

@@ -28,6 +28,7 @@ static void name_rev(struct commit *commit,
 	struct rev_name *name = (struct rev_name *)commit->util;
 	struct commit_list *parents;
 	int parent_number = 1;
+	char *to_free = NULL;
 
 	parse_commit(commit);
 
@@ -35,7 +36,7 @@ static void name_rev(struct commit *commit,
 		return;
 
 	if (deref) {
-		tip_name = xstrfmt("%s^0", tip_name);
+		tip_name = to_free = xstrfmt("%s^0", tip_name);
 
 		if (generation)
 			die("generation: %d, but deref?", generation);
@@ -53,8 +54,10 @@ copy_data:
 		name->taggerdate = taggerdate;
 		name->generation = generation;
 		name->distance = distance;
-	} else
+	} else {
+		free(to_free);
 		return;
+	}
 
 	for (parents = commit->parents;
 			parents;