ref-filter: plug memory leak in reach_filter()

21bf933928 (ref-filter: allow merged and no-merged filters, 2020-09-15)
added an early return to reach_filter().  Avoid leaking the memory of a
then unused array by postponing its allocation until we know we need it.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ref-filter.c

@@ -2239,12 +2239,14 @@ static void reach_filter(struct ref_array *array,
 {
 	struct rev_info revs;
 	int i, old_nr;
-	struct commit **to_clear = xcalloc(sizeof(struct commit *), array->nr);
+	struct commit **to_clear;
 	struct commit_list *cr;
 
 	if (!check_reachable)
 		return;
 
+	to_clear = xcalloc(sizeof(struct commit *), array->nr);
+
 	repo_init_revisions(the_repository, &revs, NULL);
 
 	for (i = 0; i < array->nr; i++) {