settings: fix the ability to register on another name server

Change-Id: Ifa7cb877c3a8ab699171810b57cf43769801e1c1
Tuleap: #1769
diff --git a/src/usernameregistrationbox.cpp b/src/usernameregistrationbox.cpp
index fc13a14..62c3c8e 100644
--- a/src/usernameregistrationbox.cpp
+++ b/src/usernameregistrationbox.cpp
@@ -209,8 +209,7 @@
 
     const auto username = gtk_entry_get_text(GTK_ENTRY(priv->entry_username));
 
-    NameDirectory::instance().lookupName(nullptr, QString(), username);
-
+    NameDirectory::instance().lookupName(priv->account, priv->account->nameServiceURL(), username);
 
     priv->lookup_timeout = 0;
     return G_SOURCE_REMOVE;