seize: set cr_errno in collect_pstree
seize: set cr_errno in collect_pstree

Before cr_errno was called from open_pid_proc(), but
now it isn't called if a root task doesn't exist.

Reported-by: Mr Jenkins
Fixes: b9b0730cb12e ("ptrace: split task_seize into seize_catch_task and seize_wait_task")
Signed-off-by: Andrew Vagin <74c05afa918858348d6db8037d82fa8124870113@openvz.org>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

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