management: Fix issuing commands with default certificate

Change-Id: I40a9b8ca1d2ff874fcd35bb39748a5d661522468
Refs: #1857
diff --git a/src/management/nfd-controller.hpp b/src/management/nfd-controller.hpp
index 4571336..3899de6 100644
--- a/src/management/nfd-controller.hpp
+++ b/src/management/nfd-controller.hpp
@@ -92,7 +92,9 @@
   {
     if (certificate.getName().empty()) { // deprecated usage
       start<Command>(parameters, onSuccess, onFailure, timeout);
+      return;
     }
+
     start<Command>(parameters, onSuccess, onFailure,
       bind(static_cast<void(KeyChain::*)(Interest&,const Name&)>(&KeyChain::sign<Interest>),
            &m_keyChain, _1, cref(certificate.getName())),