Comment 2 for bug 1726894

StacktraceTop:
 g_type_check_instance_cast (type_instance=type_instance@entry=0x56334c77dba0, iface_type=94778302508128) at ../../../../gobject/gtype.c:4057
 ext_iconsize_changed_callback (settings=0x56334bd7ed20, key=<optimized out>, user_data=0x56334c77dba0) at cc-ubuntu-panel.c:195
 g_closure_invoke (closure=0x56334b1f1e70, return_value=0x0, n_param_values=2, param_values=0x7ffd95dae2e0, invocation_hint=0x7ffd95dae260) at ../../../../gobject/gclosure.c:804
 signal_emit_unlocked_R (node=node@entry=0x56334aae6f90, detail=detail@entry=5446, instance=instance@entry=0x56334bd7ed20, emission_return=emission_return@entry=0x0, instance_and_params=instance_and_params@entry=0x7ffd95dae2e0) at ../../../../gobject/gsignal.c:3635
 g_signal_emit_valist (instance=0x56334bd7ed20, signal_id=<optimized out>, detail=5446, var_args=var_args@entry=0x7ffd95dae4b0) at ../../../../gobject/gsignal.c:3391