[glom] Dialog_Database_Preferences: Handle -1 for row/column DataModel counts.

[Murray Cumming <murrayc src gnome org>]

commit b714202f28d243b360e83806ff8a0551ef46655f
Author: Murray Cumming <murrayc murrayc com>
Date:   Tue Mar 29 17:37:08 2016 +0200

    Dialog_Database_Preferences: Handle -1 for row/column DataModel counts.

 glom/mode_design/dialog_database_preferences.cc |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/glom/mode_design/dialog_database_preferences.cc b/glom/mode_design/dialog_database_preferences.cc
index 7b91bb1..00bfdb7 100644
--- a/glom/mode_design/dialog_database_preferences.cc
+++ b/glom/mode_design/dialog_database_preferences.cc
@@ -188,8 +188,8 @@ void Dialog_Database_Preferences::load_from_document()
     return;
   }
 
-  const guint count = datamodel->get_n_rows();
-  for(guint i = 0; i < count; ++i)
+  const auto count = datamodel->get_n_rows(); // -1 means unknown.
+  for(int i = 0; i < count; ++i)
   {
     auto iter = m_model_autoincrements->append();
     Gtk::TreeModel::Row row = *iter;