I added GtkPrint support to balsa and get a reproducible crash in the cups backend when a custom paper size is selected/set.

To reproduce
- use the code snipplet below;
- in the page setup dialogue, create a custom paper size, e.g. "A4 with my margins" and select it;
- the application will crash in gtk_print_operation_run() with the following backtrace:

Program received signal SIGSEGV, Segmentation fault.

+ Trace 97298

The application does /not/ crash if a standard paper size (e.g. A4) is used.


System Details:
===============
gnome 2.16.2.1 (garnome)
gtk+ 2.10.6
cups 1.2.7
libc 2.3.4


Reproduce:
==========
The following code snipplet will crash in gtk_print_operation_run() if a custom paper size is selected:

<snip>
GtkPageSetup *page_setup;
GtkPrintSettings *settings = gtk_print_settings_new();
GtkPrintOperation *print;

page_setup = gtk_print_run_page_setup_dialog(parent, page_setup, settings);
print = gtk_print_operation_new();
gtk_print_operation_set_n_pages(print, 1);
gtk_print_operation_set_unit(print, GTK_UNIT_POINTS);
gtk_print_operation_set_use_full_page(print, FALSE);
gtk_print_operation_set_print_settings(print, settings);
gtk_print_operation_set_default_page_setup(print, page_setup);
gtk_print_operation_run(print, GTK_PRINT_OPERATION_ACTION_PRINT_DIALOG, parent, NULL);
</snip>