python3: Deal with potential NULL char*
python3: Deal with potential NULL char*

Closes #1466

Signed-off-by: Stéphane Graber <089afc6d81f66f1168a9849e15660feae286e024@ubuntu.com>

LynxChaus/lxc,aeris/lxc,thmo/lxc,GreatFruitOmsk/lxc,caglar10ur/lxc,aeris/lxc,ss1h2a3tw/lxc,federicobriata/lxc,thmo/lxc,terceiro/lxc,GreatFruitOmsk/lxc,GreatFruitOmsk/lxc,LynxChaus/lxc,federicobriata/lxc,LynxChaus/lxc,hallyn/lxc,terceiro/lxc,thmo/lxc,ss1h2a3tw/lxc,ss1h2a3tw/lxc,hallyn/lxc,hallyn/lxc,caglar10ur/lxc,aeris/lxc,terceiro/lxc,federicobriata/lxc,caglar10ur/lxc