crash in SimpleFilterModifier::get_blend_mode with a custom filter

[bbyak]

- open attached file

- select the object

- ctrl+shift+f

- in the numeric Blur field, type 0 instead of 11.3, press Enter

crash:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1235470112 (LWP 804)]
0xb69436d6 in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string ()
   from /usr/lib/libstdc++.so.6
(gdb) bt
#0 0xb69436d6 in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string ()
   from /usr/lib/libstdc++.so.6
#1 0xb7bebf22 in ustring (this=0x8, other=@0x8) at ustring.cc:291
#2 0x084f7922 in Inkscape::UI::Widget::SimpleFilterModifier::get_blend_mode (this=0xc32c538)
    at ui/widget/filter-effect-chooser.cpp:59
#3 0x084ad9e3 in Inkscape::UI::Widget::ObjectCompositeSettings::_blendBlurValueChanged (this=0xc32c418)
    at ui/widget/object-composite-settings.cpp:123
#4 0x084f8d33 in sigc::adaptor_functor<sigc::signal<void, sigc::nil, sigc::nil, sigc::nil, sigc::nil, sigc::nil, sigc::nil, sigc::nil> >::operator() (this=0xbeed7c8) at signal.h:544
#5 0xb7be7986 in Glib::SignalProxyNormal::slot0_void_callback (self=0x8, data=0xbeed798) at slot.h:440
#6 0xb7758e33 in IA__g_cclosure_marshal_VOID__VOID (closure=0xbecf818, return_value=0x0, n_param_values=1,
    param_values=0xbffc57dc, invocation_hint=0xbffc56cc, marshal_data=0x8082d8c) at gmarshal.c:77
#7 0xb774cf6f in IA__g_closure_invoke (closure=0xbecf818, return_value=0x8, n_param_values=8, param_values=0x8,
    invocation_hint=0x8) at gclosure.c:490
#8 0xb775c22c in signal_emit_unlocked_R (node=0x8e0d340, detail=0, instance=0x9936040, emission_return=0x0,
    instance_and_params=0xbffc57dc) at gsignal.c:2510
#9 0xb775d559 in IA__g_signal_emit_valist (instance=0x9936040, signal_id=130, detail=0,
    var_args=<value optimized out>) at gsignal.c:2199
#10 0xb775d8c9 in IA__g_signal_emit (instance=0x8, signal_id=8, detail=8) at gsignal.c:2243
#11 0xb78c7134 in IA__gtk_adjustment_value_changed (adjustment=0x9936040) at gtkadjustment.c:363
#12 0xb78c7221 in IA__gtk_adjustment_set_value (adjustment=0x9936040, value=0) at gtkadjustment.c:346
#13 0xb7a110b5 in IA__gtk_spin_button_update (spin_button=0x963a528) at gtkspinbutton.c:2247
#14 0xb7a11540 in gtk_spin_button_activate (entry=0x963a528) at gtkspinbutton.c:1387