Fall back to 'username' if 'user' is not given for appservice reg.

synapse/rest/client/v2_alpha/register.py

@@ -134,6 +134,8 @@ class RegisterRestServlet(RestServlet):
             # fallback to 'username' if they gave one.
             if isinstance(body.get("user"), basestring):
                 desired_username = body["user"]
+
+            if isinstance(desired_username, basestring):
                 result = yield self._do_appservice_registration(
                     desired_username, request.args["access_token"][0]
                 )