Closing the display filter editor with a filter selected
in the listview on the right, used to produce (quitting GIMP):

==32359== Invalid write of size 8
==32359==    at 0x8808DF5: g_nullify_pointer (glib/glib/gutils.c:2099)
==32359==    by 0x8358781: weak_refs_notify (glib/gobject/gobject.c:2469)
==32359==    by 0x4C3730A: gimp_color_display_dispose (gimp-2-8/libgimpwidgets/gimpcolordisplay.c:197)
==32359==    by 0x83596A7: g_object_unref (glib/gobject/gobject.c:2986)
==32359==    by 0x4C37EFA: gimp_color_display_stack_dispose (gimp-2-8/libgimpwidgets/gimpcolordisplaystack.c:150)
==32359==    by 0x83596A7: g_object_unref (glib/gobject/gobject.c:2986)
==32359==    by 0x53F1C3: gimp_display_shell_filter_set (gimp-2-8/app/display/gimpdisplayshell-filter.c:58)
==32359==    by 0x536A50: gimp_display_shell_dispose (gimp-2-8/app/display/gimpdisplayshell.c:765)