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-diff.c

@@ -190,7 +190,7 @@ static void refresh_index_quietly(void)
 	refresh_cache(REFRESH_QUIET|REFRESH_UNMERGED);
 
 	if (active_cache_changed &&
-	    !write_cache(fd, active_cache, active_nr) && !close(fd))
+	    !write_cache(fd, active_cache, active_nr))
 		commit_locked_index(lock_file);
 
 	rollback_lock_file(lock_file);