[gtkmm-documentation] command_line_handling example: on_command_line(): Correct a return code.

[Murray Cumming <murrayc src gnome org>]

commit add402d4838878913cfa80b55d0aca4cc353612c
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Sep 9 17:16:34 2015 +0200

    command_line_handling example: on_command_line(): Correct a return code.
    
    Don't return EXIT_FAILURE for what seems like a success.

 .../command_line_handling/exampleapplication.cc    |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/examples/book/application/command_line_handling/exampleapplication.cc 
b/examples/book/application/command_line_handling/exampleapplication.cc
index fbdc11a..f8e4245 100644
--- a/examples/book/application/command_line_handling/exampleapplication.cc
+++ b/examples/book/application/command_line_handling/exampleapplication.cc
@@ -181,7 +181,7 @@ int ExampleApplication::on_command_line(const Glib::RefPtr<Gio::ApplicationComma
   {
     //Open a new "document" instead:
     activate();
-    return EXIT_FAILURE;
+    return EXIT_SUCCESS;
   }
 
   Gio::Application::type_vec_files vec_files;