Render fails inelegantly if nothing routed to Scene

[firthm01]

If you have input plugins and a scene with the input plug-ins having their routing parameter set but NOT routed to the scene in REAPER, then render will take a long time and return with a message saying no audio frames were received from the scene. This is because REAPER doesn't actually run plugins which do not form part of a signal chain. Not sure if there is a way around this or to at least detect it and tell the user of the issue