[gtkmm/gtkmm-3-18] treeview_editable_cells demo: Catch exception from std::stoi

[Murray Cumming <murrayc src gnome org>]

commit b3eb1aa850c4bfc6838351d7c74f5c330ec264e0
Author: Kjell Ahlstedt <kjell ahlstedt bredband net>
Date:   Thu Feb 25 16:06:31 2016 +0100

    treeview_editable_cells demo: Catch exception from std::stoi

 demos/gtk-demo/example_treeview_editable_cells.cc |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)
---
diff --git a/demos/gtk-demo/example_treeview_editable_cells.cc 
b/demos/gtk-demo/example_treeview_editable_cells.cc
index 4bf72de..34955ee 100644
--- a/demos/gtk-demo/example_treeview_editable_cells.cc
+++ b/demos/gtk-demo/example_treeview_editable_cells.cc
@@ -7,6 +7,7 @@
  */
 
 #include <cstdlib>
+#include <iostream>
 #include <gtkmm.h>
 
 class CellItem_Product
@@ -202,7 +203,16 @@ void Example_TreeView_EditableCells::on_column_number_edited(const Glib::ustring
     if(iter)
     {
       //Convert the text to a number, using the same logic used by GtkCellRendererText when it stores 
numbers.
-      auto new_value = std::stoi(new_text);
+      int new_value = 0;
+      try
+      {
+        new_value = std::stoi(new_text);
+      }
+      catch (const std::exception& err)
+      {
+        std::cout << "Could not convert \"" << new_text << "\" to an integer. ("
+          << err.what() << ")" << std::endl;
+      }
 
       //Store the user's new text in the model:
       Gtk::TreeRow row = *iter;