This fixes the incorrect initial positioning of the tab bar (first
tab is placed out of bounds) when Kickoff is in a vertical panel
that persists until the user selects another tab manually.
BUG: 395390
And the broken layout of the tab bar (tab bar takes the whole view)
when a panel is changed from horizontal to vertical that persists
until plasmashell is restarted.
BUG: 393888