Serialize {} instead of nil
Serialize {} instead of nil

* src/apps/config/action_queue.lua: Avoid trying to serialize "nil";
  instead for apps that take no config, pass {}.

Igalia/snabb,dpino/snabb,heryii/snabb,alexandergall/snabbswitch,snabbco/snabb,alexandergall/snabbswitch,eugeneia/snabbswitch,snabbco/snabb,dpino/snabb,Igalia/snabb,Igalia/snabbswitch,alexandergall/snabbswitch,snabbco/snabb,alexandergall/snabbswitch,Igalia/snabb,eugeneia/snabb,dpino/snabb,Igalia/snabbswitch,SnabbCo/snabbswitch,heryii/snabb,dpino/snabb,Igalia/snabbswitch,Igalia/snabb,SnabbCo/snabbswitch,dpino/snabb,dpino/snabb,dpino/snabbswitch,alexandergall/snabbswitch,dpino/snabb,snabbco/snabb,dpino/snabbswitch,Igalia/snabbswitch,dpino/snabbswitch,eugeneia/snabbswitch,eugeneia/snabb,eugeneia/snabb,Igalia/snabb,eugeneia/snabb,snabbco/snabb,alexandergall/snabbswitch,Igalia/snabb,dpino/snabbswitch,Igalia/snabbswitch,alexandergall/snabbswitch,SnabbCo/snabbswitch,eugeneia/snabb,eugeneia/snabbswitch,snabbco/snabb,heryii/snabb,heryii/snabb,Igalia/snabb,alexandergall/snabbswitch,eugeneia/snabb,Igalia/snabb,SnabbCo/snabbswitch,snabbco/snabb,eugeneia/snabb,heryii/snabb,heryii/snabb,eugeneia/snabbswitch,eugeneia/snabb,snabbco/snabb