object: Force signal detail quark creation on signal connections

Otherwise handlers for detailed signals will always get called even
when the detail doesn't match the emited one.

This used to work before because g_signal_connect_closure() forces the
detail quark creation implicitly, but since we switched to
g_signal_connect_closure_by_id(), this is the right thing to do.

https://bugzilla.gnome.org/show_bug.cgi?id=691719