[glom] Check some return values.

[Murray Cumming <murrayc src gnome org>]

commit c51f2dbef33ae0a12b653edae24522c979db3663
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Dec 4 19:32:31 2014 +0100

    Check some return values.
    
    Found by Coverity Scan.

 glom/base_db.cc                             |    7 ++++++-
 glom/mode_design/users/dialog_users_list.cc |    6 +++++-
 2 files changed, 11 insertions(+), 2 deletions(-)
---
diff --git a/glom/base_db.cc b/glom/base_db.cc
index 1cffa84..37577e6 100644
--- a/glom/base_db.cc
+++ b/glom/base_db.cc
@@ -266,9 +266,14 @@ sharedptr<Field> Base_DB::change_column(const Glib::ustring& table_name, const s
   ConnectionPool* connection_pool = ConnectionPool::get_instance();
   sharedptr<Field> result = check_field_change_constraints(field_old, field);
 
+  //TODO: change_column() doesn't throw any exception.
   try
   {
-    connection_pool->change_column(table_name, field_old, result);
+    if(!connection_pool->change_column(table_name, field_old, result))
+    {
+      std::cerr << G_STRFUNC << ": change_column() failed." << std::endl;
+      return sharedptr<Field>();
+    }
   }
   catch(const Glib::Error& ex)
   {
diff --git a/glom/mode_design/users/dialog_users_list.cc b/glom/mode_design/users/dialog_users_list.cc
index 6a2faed..8cf6d60 100644
--- a/glom/mode_design/users/dialog_users_list.cc
+++ b/glom/mode_design/users/dialog_users_list.cc
@@ -266,7 +266,11 @@ void Dialog_UsersList::on_button_user_new()
   if(response != Gtk::RESPONSE_OK)
     return;
 
-  DbUtils::add_user(get_document(), user, password, m_combo_group->get_active_text() /* group */);
+  if(!DbUtils::add_user(get_document(), user, password, m_combo_group->get_active_text() /* group */))
+  {
+    std::cerr << G_STRFUNC << ": add_user() failed." << std::endl;
+  }
+
   fill_list();
 }