If the \a to widget was already part of a layout it would be removed from
the layout. This happened because the function that was supposed to
perform this removal was called after we had done the replacement.
QLayout::addChildWidget() should therefore be called first.  This is also
documented in QLayout::addChildWidget()

Change-Id: Ie718935a14ebad81827fad962920e930263c05b8
Task-number: QTBUG-37724
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>