Fix comboentry size calculation on first show
Fix comboentry size calculation on first show

Call show_all before calculating the size or else, even forcing the treeview to
realize itself, it will still report a smaller height for its cells that they
really have. Also, there's no need to call it on every adjust_position, just
once on popup is enough.

Change-Id: Ibc11947494570c6d86e1e16863e250286f531ae1

stoq/kiwi