cgroups/fs: fix NPE on Destroy than no cgroups are set
cgroups/fs: fix NPE on Destroy than no cgroups are set

Currently Manager accepts nil cgroups when calling Apply, but it will panic then trying to call Destroy with the same config.

Signed-off-by: Denys Smirnov <d29de71aea38aad3a87d486929cb0aad173ae612@sourced.tech>

cyphar/runc,crosbymichael/runc,laijs/runc,rhatdan/runc,wking/runc,kolyshkin/runc,crosbymichael/runc,kolyshkin/runc,adrianreber/runc,wking/runc,cyphar/runc,mikebrow/runc,xiaochenshen/runc,cyphar/runc,mheon/runc,crosbymichael/runc,stefanberger/runc,rhatdan/runc,estesp/runc,xiaochenshen/runc,mheon/runc,stefanberger/runc,dqminh/runc,estesp/runc,opencontainers/runc,kolyshkin/runc,dqminh/runc,opencontainers/runc,dqminh/runc,justincormack/runc,xiaochenshen/runc,opencontainers/runc,stefanberger/runc,kolyshkin/runc,rhatdan/runc,adrianreber/runc,mYmNeo/runc,mYmNeo/runc,adrianreber/runc,mikebrow/runc,laijs/runc,estesp/runc,laijs/runc,justincormack/runc,mikebrow/runc,mYmNeo/runc,dqminh/runc,rhatdan/runc,mheon/runc,opencontainers/runc,wking/runc,justincormack/runc