An interference of sigreturn_restore rework patches and vm_open callback ones
has lead to the situation when vme for restorer has already been copied to
rst-mem, but sysv shmem vm_open tried to modify previously seen vmes.

Fix this by copying vme-s to restorer late, but still before sigreturn_restore.
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>