THRIFT-4854 oneway calls do not work over HTTP
Client: netstd
Patch: Jens Geyer

This closes #1790
diff --git a/lib/netstd/Thrift/Transport/Server/THttpServerTransport.cs b/lib/netstd/Thrift/Transport/Server/THttpServerTransport.cs
index b5a500c..056300c 100644
--- a/lib/netstd/Thrift/Transport/Server/THttpServerTransport.cs
+++ b/lib/netstd/Thrift/Transport/Server/THttpServerTransport.cs
@@ -100,12 +100,13 @@
 
                 while (await Processor.ProcessAsync(input, output, cancellationToken))
                 {
+                    if (!context.Response.HasStarted)  // oneway method called
+                        await context.Response.Body.FlushAsync(cancellationToken);
                 }
             }
             catch (TTransportException)
             {
-                // Client died, just move on
-                if (!context.Response.HasStarted)
+                if (!context.Response.HasStarted)  // if something goes bust, let the client know
                     context.Response.StatusCode = 500;
             }
             finally