Remove no-op

[hexagonrecursion]

This two lines of code used to have a purpose, but refactroing (8e01a20) turned them into a no-op

colobot/CBot/src/CBot/CBotStack.cpp

Lines 599 to 600 in c56d240

	res = m_prog->GetExternalCalls()->DoCall(nullptr, nullptr, ppVar, this, rettype);
	if (res >= 0) return res;

is no-op because DoCall(nullptr, ...) returns -1

colobot/CBot/src/CBot/CBotExternalCall.cpp

Lines 74 to 78 in c56d240

	int CBotExternalCallList::DoCall(CBotToken* token, CBotVar* thisVar, CBotVar** ppVar, CBotStack* pStack,
	const CBotTypResult& rettype)
	{
	if (token == nullptr)
	return -1;