Call completeStream only once on failure.

jetty-core/jetty-server/src/main/java/org/eclipse/jetty/server/internal/HttpChannelState.java

@@ -1576,7 +1576,7 @@ public void succeeded()
                     if (!stream.isCommitted())
                         errorResponse = new ErrorResponse(request);
                     else
-                        completeStream = true;
+                        completeStream = httpChannelState._handling == null;
                 }
             }