Balsa 2.2.3 crash when turning "subscribed folders only" off/on

[Miquel van Smoorenburg <miquels cistron nl>]

Settings -> preferences -> IMAP server -> "remote IMAP folder".

I have "Subscribed folders only" turned on. When I turn it off,
and click "Update", balsa crashes.

Under gdb it didn't crash when I turned it off, but when I turned
it back on and clicked "Update" balsa did crash:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 1097430016 (LWP 21522)]
0x41051632 in g_type_check_instance_cast () from /usr/lib/libgobject-2.0.so.0
(gdb) where
#0  0x41051632 in g_type_check_instance_cast ()
   from /usr/lib/libgobject-2.0.so.0
#1  0x080e05a9 in libbalsa_mailbox_imap_update_url (mailbox=0x827f2d0)
    at mailbox_imap.c:312
#2  0x080d9b2f in libbalsa_VOID__POINTER_INT (closure=0x82818c0,
    return_value=0x0, n_param_values=3, param_values=0xbfffe600,
    invocation_hint=0xbfffe4f8, marshal_data=0x0) at libbalsa-marshal.c:402
#3  0x41033c20 in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#4  0x41047c25 in g_signal_emit_by_name () from /usr/lib/libgobject-2.0.so.0
#5  0x41046be7 in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#6  0x41046ee4 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#7  0x080fc03a in libbalsa_server_set_host (server=0x41062bc8,
    host=0x6e6f7274 <Address 0x6e6f7274 out of bounds>, use_ssl=1852797556)
    at server.c:217
#8  0x0808e1ea in folder_conf_clicked_ok (fcw=0x85deda0) at folder-conf.c:178
#9  0x0808e026 in folder_conf_response (dialog=0x85e11e0, response=-5,
    cdd=0x85deda0) at folder-conf.c:111
#10 0x4104845e in g_cclosure_marshal_VOID () from /usr/lib/libgobject-2.0.so.0
#11 0x41033c20 in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#12 0x41047c25 in g_signal_emit_by_name () from /usr/lib/libgobject-2.0.so.0
#13 0x41046be7 in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#14 0x41046ee4 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#15 0x40be855c in gtk_dialog_response () from /usr/lib/libgtk-x11-2.0.so.0
#16 0x40be7bdc in gtk_dialog_new_with_buttons ()
   from /usr/lib/libgtk-x11-2.0.so.0
#17 0x41048121 in g_cclosure_marshal_VOID__VOID ()
   from /usr/lib/libgobject-2.0.so.0
#18 0x41033c20 in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#19 0x41047c25 in g_signal_emit_by_name () from /usr/lib/libgobject-2.0.so.0
#20 0x41046be7 in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#21 0x41046ee4 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#22 0x40b9c075 in gtk_button_clicked () from /usr/lib/libgtk-x11-2.0.so.0
#23 0x40b9d08b in _gtk_button_paint () from /usr/lib/libgtk-x11-2.0.so.0
#24 0x41048121 in g_cclosure_marshal_VOID__VOID ()
   from /usr/lib/libgobject-2.0.so.0
#25 0x41033fb7 in g_cclosure_new_swap () from /usr/lib/libgobject-2.0.so.0
#26 0x41033c20 in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#27 0x4104744e in g_signal_emit_by_name () from /usr/lib/libgobject-2.0.so.0
#28 0x41046be7 in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#29 0x41046ee4 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#30 0x40b9bfc5 in gtk_button_released () from /usr/lib/libgtk-x11-2.0.so.0
#31 0x40b9cf0b in _gtk_button_paint () from /usr/lib/libgtk-x11-2.0.so.0
#32 0x40c58b64 in _gtk_marshal_BOOLEAN__BOXED ()
   from /usr/lib/libgtk-x11-2.0.so.0
#33 0x41033fb7 in g_cclosure_new_swap () from /usr/lib/libgobject-2.0.so.0
#34 0x41033c20 in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#35 0x41047655 in g_signal_emit_by_name () from /usr/lib/libgobject-2.0.so.0
#36 0x410469be in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#37 0x41046ee4 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#38 0x40d57427 in gtk_widget_send_expose () from /usr/lib/libgtk-x11-2.0.so.0
#39 0x40c57102 in gtk_propagate_event () from /usr/lib/libgtk-x11-2.0.so.0
#40 0x40c55e56 in gtk_main_do_event () from /usr/lib/libgtk-x11-2.0.so.0
#41 0x40f60175 in _gdk_events_queue () from /usr/lib/libgdk-x11-2.0.so.0
#42 0x4108c902 in g_main_depth () from /usr/lib/libglib-2.0.so.0
#43 0x4108d9f8 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#44 0x4108dd30 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#45 0x4108e373 in g_main_loop_run () from /usr/lib/libglib-2.0.so.0
#46 0x40c55713 in gtk_main () from /usr/lib/libgtk-x11-2.0.so.0
#47 0x0809fbfe in main (argc=1, argv=0xbffffa74) at main.c:612