Code review comment for lp:~and471/inkscape/ocal-dialog-improvements

Found another crasher, reproduced on Ubuntu 10.10 and Windows XP.

Steps:
1. Launch OCAL import.
2. Search something (used "skull").
3. Select the first result in the search list.
4. Search something else (used "pirate").

Backtrace:
Program received signal SIGSEGV, Segmentation fault.
0x005d3430 in Gtk::TreePath::get_indices() const () from /usr/lib/libgtkmm-2.4.so.1
(gdb) bt
#0 0x005d3430 in Gtk::TreePath::get_indices() const () from /usr/lib/libgtkmm-2.4.so.1
#1 0x0853b32f in Inkscape::UI::Dialog::OCAL::ImportDialog::on_list_results_selection_changed() ()
#2 0x08547ce7 in sigc::bound_mem_functor0<void, Inkscape::UI::Dialog::OCAL::ImportDialog>::operator()() const ()
#3 0x085472c9 in sigc::adaptor_functor<sigc::bound_mem_functor0<void, Inkscape::UI::Dialog::OCAL::ImportDialog> >::operator()() const ()
#4 0x0854617b in sigc::internal::slot_call0<sigc::bound_mem_functor0<void, Inkscape::UI::Dialog::OCAL::ImportDialog>, void>::call_it(sigc::internal::slot_rep*) ()
#5 0x00c6d19b in Glib::SignalProxyNormal::slot0_void_callback(_GObject*, void*) () from /usr/lib/libglibmm-2.4.so.1
#6 0x019fef2c in g_cclosure_marshal_VOID__VOID (closure=0xaa6ed88, return_value=0x0, n_param_values=1, param_values=0xab25508,
    invocation_hint=0xbfffe610, marshal_data=0x8083d10) at /build/buildd/glib2.0-2.26.1/gobject/gmarshal.c:79
#7 0x019ef412 in g_closure_invoke (closure=0xaa6ed88, return_value=0x0, n_param_values=1, param_values=0xab25508,
    invocation_hint=0xbfffe610) at /build/buildd/glib2.0-2.26.1/gobject/gclosure.c:766
#8 0x01a05f78 in signal_emit_unlocked_R (node=<value optimised out>, detail=<value optimised out>, instance=0xaa84220,
    emission_return=0x0, instance_and_params=0xab25508) at /build/buildd/glib2.0-2.26.1/gobject/gsignal.c:3322
#9 0x01a06fac in g_signal_emit_valist (instance=0xaa84220, signal_id=318, detail=0, var_args=0xbfffe848 "P\aA\n")
    at /build/buildd/glib2.0-2.26.1/gobject/gsignal.c:2983
#10 0x01a07275 in g_signal_emit_by_name (instance=0xaa84220, detailed_signal=0xbce996 "changed")
    at /build/buildd/glib2.0-2.26.1/gobject/gsignal.c:3077