If the signal takes a value, we pass the current value of the property
to it.
As we now use eager evaluation, accessing the current value is now
possible.
Change-Id: I5e6947a6575bfa8ca5143f56620c645d4750a686
Reviewed-by: Andreas Buhr <andreas.buhr@qt.io>
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>