[gtkada] Locale_To_UTF8 problem

[Manuel Op de Coul]

The function
Locale_To_UTF8 (OS_String : String) return String in
package Glib.Convert raises the exception 
Interfaces.C.Strings.Dereference_Error when the
input string contains a non-ascii Latin-1 character.

This happens on a number of Linux systems when the
value of LANG=C for example.

I see in the package body that the Error parameter is
ignored.

What causes this exception to be raised, and could
GtkAda be improved to handle this situation more
gracefully?

Thanks,

Manuel