Fix duplicate message issue in Websocket impl

Summary: Missed an else on the if statement, causing it to duplicate websocket messages.

Reviewed By: passy

Differential Revision: D21256794

fbshipit-source-id: ea4abb88723a052a3490b930420ee6b005447c81

desktop/app/src/server.tsx

@@ -213,8 +213,9 @@ class Server extends EventEmitter {
                 const message = JSON.stringify(parsed.payload);
                 if (resolvedClient) {
                   resolvedClient.onMessage(message);
+                } else {
+                  client.then((c) => c.onMessage(message));
                 }
-                client.then((c) => c.onMessage(message));
               }
             });
             break;