don't dereference a NULL c->lxc_conf
don't dereference a NULL c->lxc_conf

Commit 37cf711b added a destroy hook, but when it checks
at destroy time whether that hook exists, it assumes that
c->lxc_conf is good.  In fact lxc_conf can be NULL, so check
for that.

Signed-off-by: Serge Hallyn <3df611b026e4639bee8aef7a4beb2e39fcebb313@ubuntu.com>
Acked-by: Stéphane Graber <089afc6d81f66f1168a9849e15660feae286e024@ubuntu.com>

hfuCN/lxc,JohnPeacockMessageSystems/lxc,federicobriata/lxc,federicobriata/lxc,caglar10ur/lxc,lisongmin/lxc,terceiro/lxc,bostjan/lxc,major/lxc,rldleblanc/lxc,sapun/lxc,virajs/lxc,fwilson42/lxc,lisongmin/lxc,sapun/lxc,efiop/lxc,armcc/lxc,hallyn/lxc,GreatFruitOmsk/lxc,bmoar/lxc,caglar10ur/lxc,cjwatson/lxc,rldleblanc/lxc,jirislaby/lxc,aeris/lxc,ysbnim/lxc,thmo/lxc,armcc/lxc,akshaykarle/lxc,raspberrypython/lxc,jirislaby/lxc,LynxChaus/lxc,LynxChaus/lxc,Pelagicore/lxc,rldleblanc/lxc,DarknessBeforeDawn/lxc,sapun/lxc,efiop/lxc,bmoar/lxc,cjwatson/lxc,rowhit/lxc,federicobriata/lxc,thmo/lxc,GreatFruitOmsk/lxc,bostjan/lxc,yubo/lxc,aeris/lxc,bmoar/lxc,ysbnim/lxc,GreatFruitOmsk/lxc,ioops/lxc,LynxChaus/lxc,tych0/lxc,akshaykarle/lxc,efiop/lxc,Distrotech/lxc,christiaan/lxc,hfuCN/lxc,ksperis/lxc,terceiro/lxc,ss1h2a3tw/lxc,ecarrara/lxc,QingweiPeterLan/cs188-lxc,QingweiPeterLan/cs188-lxc,ioops/lxc,DarknessBeforeDawn/lxc,lazy404/lxc,szaszg/lxc,christiaan/lxc,codebauss/lxc,hfuCN/lxc,ecarrara/lxc,yubo/lxc,Pelagicore/lxc,QingweiPeterLan/cs188-lxc,virajs/lxc,terceiro/lxc,ecarrara/lxc,Pelagicore/lxc,hallyn/lxc,raspberrypython/lxc,virajs/lxc,ksperis/lxc,yubo/lxc,codebauss/lxc,major/lxc,major/lxc,akshaykarle/lxc,codebauss/lxc,szaszg/lxc,tych0/lxc,lazy404/lxc,hallyn/lxc,thmo/lxc,rowhit/lxc,Ponce/lxc,lisongmin/lxc,rowhit/lxc,christiaan/lxc,JohnPeacockMessageSystems/lxc,raspberrypython/lxc,tych0/lxc,ss1h2a3tw/lxc,aeris/lxc,DarknessBeforeDawn/lxc,ss1h2a3tw/lxc,Distrotech/lxc,Ponce/lxc,armcc/lxc,fwilson42/lxc,bostjan/lxc,jirislaby/lxc,ksperis/lxc,caglar10ur/lxc,JohnPeacockMessageSystems/lxc,cjwatson/lxc,Distrotech/lxc,Ponce/lxc,lazy404/lxc,ysbnim/lxc,szaszg/lxc,fwilson42/lxc,ioops/lxc