[#4067] Fix gtk-critical warnings for new accounts

sflphone-client-gnome/src/config/accountconfigdialog.c

@@ -74,7 +74,7 @@ GtkWidget * entryMailbox;
 GtkWidget * entryUseragent;
 GtkWidget * entryResolveNameOnlyOnce;
 GtkWidget * expireSpinBox;
-GtkListStore * credentialStore;
+GtkListStore * credentialStore = NULL;
 GtkWidget * deleteCredButton;
 GtkWidget * treeViewCredential;
 // GtkWidget * scrolledWindowCredential;
@@ -261,13 +261,15 @@ static void update_credential_cb (GtkWidget *widget, gpointer data UNUSED)
     GtkTreeIter iter;
 
     if (credentialStore) {
-        gtk_tree_model_get_iter_from_string ( (GtkTreeModel *) credentialStore, &iter, "0");
+        if (gtk_tree_model_get_iter_from_string ( (GtkTreeModel *) credentialStore, &iter, "0")) {
             gint column = GPOINTER_TO_INT (g_object_get_data (G_OBJECT (widget), "column"));
             // g_print ("set password to %s\n", (gchar *) gtk_entry_get_text(GTK_ENTRY(widget)));
             gtk_list_store_set (GTK_LIST_STORE (credentialStore), &iter, column, (gchar *) gtk_entry_get_text (GTK_ENTRY (widget)), -1);
         }
     }
 
+}
+
 static GtkWidget* create_basic_tab (account_t **a)
 {