Error when task force has no country specified should be handled better

[birgersp]

Currently, creating a new task force without setting the country ID (either manually or automatically) results in an error. When creating a task force, then error should be handled differently.

autogft_Setup:new()
:addBaseZone("BLUE_BASE")
:addControlZone("OBJECTIVE_WEST")
:addControlZone("OBJECTIVE_EAST")
:setCountry(country.id.USA)
:setSkill("High")
:setSpeed(30)
:setMaxRouteDistance(5)
:setAdvancementTimer(300)
:addTaskGroup():addUnits(6, "Leopard-2"):addUnits(8, "Marder")
:addTaskGroup():addUnits(2, "Gepard"):addUnits(2, "M1097 Avenger")
:setReinforceTimer(300)

--Red Ground Forces
autogft_Setup:new()
:addBaseZone("RED_BASE")
:addControlZone("OBJECTIVE_EAST")
:addControlZone("OBJECTIVE_WEST")
:addTaskGroup():addUnits(8, "T-72B"):addUnits(10, "BMP-2")
:addTaskGroup():addUnits(4, "ZSU-23-4 Shilka"):addUnits(2, "Strela-10M3")
:setSkill("High")
:setSpeed(30)
:setMaxRouteDistance(5)
:setAdvancementTimer(300)
:setReinforceTimer(300)```