[Window List]Fix initial focus
Summary:
Now arrow key nav works when opening a panel applet via keyboard
shortcut.
Fixes the same problem as D15856
Test Plan:
Open the window list applet with a keyboard shortcut, move
around with the up and down arrows
Reviewers: Plasma, hein, mart
Reviewed By: Plasma, mart
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D16053