vzctl set --devices --save: do not segfault

This is an addition to commit ea64ee6b9. It fixes segfault
in store_dev() when --devices option was used.

Signed-off-by: Kir Kolyshkin <kir@openvz.org>
(cherry picked from commit ba865963f38c747b0732db0ff8401ff5184db1b8)
1 file changed