applets/kickoff: make list delegate heights consistent
When the description label is not present, the title label increases its implicit height to attempt to match it so that all list delegates have the same height. However it was using a faulty calculation by simply doubling its own implicitHeight. This would have worked if both labels had the same height, but they don't: the description label uses the small font, so it's shorter.
We can fix this by using the description label's actual height instead of approximating it incorrectly.
BUG: 479287 FIXED-IN: 6.0