Handle live resource not being there even if it shouldn't be missing

* I was a little conflicted about this, as the resources present in logs
  should be determinable - if a function marks it as referenced then the
  serialised version of that function should expect the resource to be
  present, and if it's not then there's a bug and we can't properly replay.
* However I am tempted to say that instead of likely crashing due to an
  invalid NULL pointer suddenly appearing somewhere, we should instead try
  to continue even if a resource isn't available.