seize: collect_pstree -- Add missing error sign return
seize: collect_pstree -- Add missing error sign return

If we can't freeze process don't forget to return
error sign, otherwise we continue operating over
nonfrozen processes, leading into various errors.

Signed-off-by: Cyrill Gorcunov <7a1ea01eee6961eb1e372e3508c2670446d086f4@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@virtuozzo.com>

KKoukiou/criu-remote,KKoukiou/criu-remote,KKoukiou/criu-remote,KKoukiou/criu-remote,KKoukiou/criu-remote,KKoukiou/criu-remote