ComboBox: Editable CBs and popups don't go well together

Change-Id: I387521908df378d0e4f75b546999ff37b6cdae13
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
ComboBox: Fix selected item alignment

We seem to receive a size change later that we used to, and this exposed
a bug were the popup would always be aligned on the first item.

Change-Id: I7b7b4ca5fcff969c3b492419cab7447170a2c3f5
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>