pstee: fix memory corrupation
pstee: fix memory corrupation

The pstree_item for helpers is allocated without rst_info.
Before this patch prepare_fd_pid was executed for such items and
touched rst_info.

Signed-off-by: Andrey Vagin <74c05afa918858348d6db8037d82fa8124870113@openvz.org>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

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