Toggling ULevelStreaming::bShouldBeVisible causes replication errors

Looks like the replication system doesn't properly account for bShouldBeVisible. Once a level has be marked bShouldBeVisible=false on the server, the level is completely cleaned up and all actor channels are permanently closed.

The actor channels should be recreated when the level becomes visible again.

1. Open the attached project.
2. Ensure settings are Single Process, Dedicated Server.
3. Set the LogNet log level to verbose. In editor, bring up console and enter:

   log lognet verbose

4. PIE
5. Press 1 to toggle visibility until it is off (initially it will report being on).
6. Wait a few seconds.
7. Press 1 to toggle visibility on.

Expected: When visibility is re-enabled the streamed level is visible and networking resumes with no issues.

Actual: When visibility is re-enabled replication errors occur because the Actor channels have been destroyed:

LogNet: Server connection received: ActorChannelFailure
LogNet:Warning: UActorChannel::ProcessBunch: SerializeNewActor failed to find/spawn actor.