[KonsoleProfiles applet] 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 konsole profile applet with a keyboard shortcut, move
around with the up and down arrows

Reviewers: Plasma, davidedmundson, hein, mart

Reviewed By: Plasma, mart

Subscribers: ngraham, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D15963