add_existing(): do not retain a reference to sha1

Its lifetime is not guaranteed, so make a copy.  Free the memory when
the string_list is cleared.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fetch.c

@@ -571,7 +571,8 @@ static int add_existing(const char *refname, const unsigned char *sha1,
 {
 	struct string_list *list = (struct string_list *)cbdata;
 	struct string_list_item *item = string_list_insert(list, refname);
-	item->util = (void *)sha1;
+	item->util = xmalloc(20);
+	hashcpy(item->util, sha1);
 	return 0;
 }
 
@@ -636,7 +637,7 @@ static void find_non_local_tags(struct transport *transport,
 		item = string_list_insert(&remote_refs, ref->name);
 		item->util = (void *)ref->old_sha1;
 	}
-	string_list_clear(&existing_refs, 0);
+	string_list_clear(&existing_refs, 1);
 
 	/*
 	 * We may have a final lightweight tag that needs to be
@@ -782,7 +783,7 @@ static int do_fetch(struct transport *transport,
 	}
 
  cleanup:
-	string_list_clear(&existing_refs, 0);
+	string_list_clear(&existing_refs, 1);
 	return retcode;
 }