revision.c: --indexed-objects add objects from all worktrees

revision.c: --indexed-objects add objects from all worktrees

This is the result of single_worktree flag never being set (no way to up
until now). To get objects from current index only, set single_worktree.

The other add_index_objects_to_pending's caller is mark_reachable_objects()
(e.g. "git prune") which also mark objects from all indexes.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>