fallback support

Inspectron.Epson/PrintServer/JobSources/SingleJobSource.cs

@@ -11,6 +11,11 @@ public class SingleJobSource: IPrintJobSource
     }
 
     private Channel<PrintJob> _channel = Channel.CreateUnbounded<PrintJob>();
+    public Task StartAsync()
+    {
+        return Task.CompletedTask;
+    }
+
     public async Task<PrintJob> GetNextJobAsync(CancellationToken cancellationToken)
     {
         return await _channel.Reader.ReadAsync(cancellationToken);