Fixed verification threshold when set to 0
Fixed verification threshold when set to 0

no issue

- if the verification threshold is 0, `_.get(..)` becomes falsy so we
  fallback to Infinity
- this is not correct - we only want to default to Infinity if the value
  is not set
- this commit explicitly compares the config value to `undefined` and sets
  the fallback accordingly

TryGhost/Ghost,ErisDS/Ghost,ErisDS/Ghost,TryGhost/Ghost,e10/Ghost,TryGhost/Ghost,e10/Ghost,ErisDS/Ghost