ErrorFrames propagating upstream from downstream processors (e.g. TTS) would
enter the ServiceSwitcher via process_frame, traverse the active service sub-pipeline,
and reach push_frame where they incorrectly triggered failover. Now only errors whose
processor is one of the managed services trigger handle_error. Also fix the log in
handle_error to attribute errors to the actual source processor rather than the
current active_service.
Closes#4139
fdbdbc8be3