around line 265 or so : 

_spawned = true;

int spawnedCount = 0;
for (int i = 0; i < _zombiesConfig.Population; i++)
{
SpawnZombie();
spawnedCount++;
yield return _waitTenthSecond;
}

DaysSinceLastSpawn = 0;

_currentCoroutine = null;

if (_config.Broadcast.DoBroadcast && _spawned)
{
Broadcast("ChatBroadcast", spawnedCount);
}
}

that was a mix of code taken from the fixed version that @56kFM posted about a year ago. 

Hope that helps!