wait until response is flushed before unsubscribing from broker

I am not sure why this works, but it seems to. I have been trying to
enable the scaffolder and found that when I view a task in progress or
complete that the task just sits with the text "Waiting for logs...".

This is a hunch.

Signed-off-by: Brian Fletcher <brian@roadie.io>

plugins/scaffolder-backend/src/service/router.ts

@@ -233,17 +233,19 @@ export async function createRouter(
             );
           }
 
+          let shouldUnsubscribe = false;
           for (const event of events) {
             res.write(
               `event: ${event.type}\ndata: ${JSON.stringify(event)}\n\n`,
             );
             if (event.type === 'completion') {
-              unsubscribe();
+              shouldUnsubscribe = true;
               // Closing the event stream here would cause the frontend
               // to automatically reconnect because it lost connection.
             }
           }
           res.flush();
+          if (shouldUnsubscribe) unsubscribe();
         },
       );
       // When client closes connection we update the clients list