Segfault just by clicking white box

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Just clicking the white area in the bottom left of the image below causes a segmentation fault.

Thread 1 "kernagic" received signal SIGSEGV, Segmentation fault.
0x00005555555638b8 in index_press_cb (widget=0x5555558c5650, event=0x55555597d6a0, data=0x0)
    at ui-gtk.c:631
631       for (l = list; l->next; l = l->next)
(gdb) bt
#0  0x00005555555638b8 in index_press_cb
    (widget=0x5555558c5650, event=0x55555597d6a0, data=0x0) at ui-gtk.c:631
#1  0x0000155554e187cc in  () at /usr/lib/libgtk-x11-2.0.so.0
#2  0x000015555462ae75 in g_closure_invoke () at /usr/lib/libgobject-2.0.so.0
#3  0x0000155554617fd5 in  () at /usr/lib/libgobject-2.0.so.0
#4  0x000015555461b76d in g_signal_emit_valist () at /usr/lib/libgobject-2.0.so.0
#5  0x000015555461d080 in g_signal_emit () at /usr/lib/libgobject-2.0.so.0
#6  0x0000155554f33235 in  () at /usr/lib/libgtk-x11-2.0.so.0
#7  0x0000155554e16a0e in gtk_propagate_event () at /usr/lib/libgtk-x11-2.0.so.0
#8  0x0000155554e16e43 in gtk_main_do_event () at /usr/lib/libgtk-x11-2.0.so.0
#9  0x0000155554a8fd5e in  () at /usr/lib/libgdk-x11-2.0.so.0
#10 0x000015555453d7bf in g_main_context_dispatch () at /usr/lib/libglib-2.0.so.0
#11 0x000015555453f739 in  () at /usr/lib/libglib-2.0.so.0
#12 0x00001555545406d2 in g_main_loop_run () at /usr/lib/libglib-2.0.so.0
#13 0x0000155554e15df3 in gtk_main () at /usr/lib/libgtk-x11-2.0.so.0
#14 0x00005555555653c7 in ui_gtk (argc=1, argv=0x7fffffffe1a8) at ui-gtk.c:1042
#15 0x000055555555e195 in main (argc=1, argv=0x7fffffffe1a8) at kernagic.c:706