Improve use of lockfile API

Remove remaining double close(2)'s.  i.e. close() before
commit_locked_index() or commit_lock_file().

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-add.c

@@ -259,7 +259,7 @@ int cmd_add(int argc, const char **argv, const char *prefix)
  finish:
 	if (active_cache_changed) {
 		if (write_cache(newfd, active_cache, active_nr) ||
-		    close(newfd) || commit_locked_index(&lock_file))
+		    commit_locked_index(&lock_file))
 			die("Unable to write new index file");
 	}