Fix broken layout that results from making key visible after startup

The RowLayout that contained the key that was made visible seemed to
get an implicitHeight, where all the other rows had implicitHeights of
0. The RowLayouts fill the width and height of their parent (a
ColumnLayout), which means that the implicitHeight won't be used as
long as its small enough; it's just there to prevent rows from getting
large implicitHeights.

Task-number: QTBUG-54953
Change-Id: Ic7a8a6f00f03a4ea8a05abf69cfedcf168c919d7
Reviewed-by: Jan Arve Sæther <jan-arve.saether@theqtcompany.com>