GUACAMOLE-201: Occasionally verify client responsiveness when intercepting streams.

guacamole/src/main/webapp/app/rest/services/tunnelService.js

@@ -215,6 +215,11 @@ angular.module('rest').factory('tunnelService', ['$injector',
             document.body.removeChild(iframe);
         };
 
+        // Acknowledge (and ignore) any received blobs
+        stream.onblob = function acknowledgeData() {
+            stream.sendAck('OK', Guacamole.Status.Code.SUCCESS);
+        };
+
         // Automatically remove iframe from DOM a few seconds after the stream
         // ends, in the browser does NOT fire the "load" event for downloads
         stream.onend = function downloadComplete() {